This suggests that this serine residue is a potential phosphorylation site for the dual-specificity tyrosine phosphorylated and regulated kinase 2 (DYRK2), a prototypical proline-directed kinase. Its phosphorylation may prime a highly conserved preceding serine residue (S617 in rat) to be phosphorylated by glycogen synthase kinase 3 β (GSK3β). Therefore, we investigated the effect of DYRK2 on ENaC activity in outside-out patches of Xenopus laevis oocytes heterologously expressing rat ENaC. DYRK2 included in the pipette solution significantly increased ENaC activity. In contrast, GSK3β had an inhibitory effect. Replacing S621 in αENaC with alanine (S621A) abolished the effects of both kinases. A S617A mutation reduced the inhibitory effect of GKS3β but did not prevent ENaC activation by DYRK2. Our findings suggest that phosphorylation of S621 activates ENaC and primes S617 for subsequent phosphorylation by GSK3β resulting in channel inhibition. In proof-of-concept experiments, we demonstrated that DYRK2 can also stimulate ENaC currents in microdissected mouse distal nephron, whereas GSK3β inhibits the currents.How phosphorylation of the epithelial sodium channel (ENaC) contributes to its regulation is incompletely understood. Previously, we demonstrated that in outside-out patches ENaC activation by serum- and glucocorticoid-inducible kinase isoform 1 (SGK1) was abolished by mutating a serine residue in a putative SGK1 consensus motif RXRXX(S/T) in the channel’s α-subunit (S621 in rat). Interestingly, this serine residue is followed by a highly conserved proline residue rather than by a hydrophobic amino acid thought to be required for a functional SGK1 consensus motif according to  Each su mammals , 49, 65.At the cellular level, ENaC regulation involves a complex interplay of extracellular factors and intracellular signal transduction pathways including a number of protein kinases , 37, 65.Xenopus laevis oocytes, the stimulatory effect of coexpressed SGK1 on ENaC whole-cell currents can be attributed mainly to an increased channel abundance at the cell surface [In  surface , 21, 62. surface , 46. Thi surface . In addi surface . This di surface , 21. Ori surface , 39 in tinvitro studies that the RXRXX(S/T) motif has to be followed by a bulky hydrophobic residue to become a preferred SGK/PKB consensus motif [Presently, it remains an open question whether SGK1 and PKBα directly phosphorylate the channel at the identified phosphorylation site S621. Indeed, it is conceivable that the stimulatory effect of the recombinant kinases is mediated by modifying the activity of endogenous kinases or phosphatases present in the patch, thereby indirectly favoring channel phosphorylation at this site. Thus, SGK1 and PKBα may not phosphorylate the channel directly but may mediate their effect by activating or inhibiting an endogenous kinase or phosphatase, respectively. This hypothesis is supported by evidence from us motif . In contus motif  but a po618RYWSP622  is a prototypical proline-directed kinase and a member of a family comprising at least seven mammalian isoforms . DYRK2 hPS) or phosphothreonine residue (PT) is present four residues C-terminal to the site of GSK3β phosphorylation. Thus, a typical GSK3β recognition motif has the following sequence: SXXX(PS/PT) [Interestingly, DYRK2 phosphorylates several substrates which are subsequently recognized and further phosphorylated by the glycogen synthase kinase 3 β (GSK3β) . Among tX(PS/PT) , 24. ThiXenopus laevis oocytes using the outside-out patch clamp technique and site-directed mutagenesis. To confirm the oocyte findings in proof-of-concept experiments in native renal tissue, we also studied the effects of recombinant DYRK2 and GSK3β on ENaC currents in patch-clamp recordings from microdissected mouse distal nephron.Therefore, the aim of the present study was to investigate whether DYRK2 and GSK3β can affect ENaC function and whether this involves the two adjacent serine residues S621 and S617 located in the α-subunit of rat ENaC. For this purpose, we tested the effects of recombinant DYRK2 and GSK3β on rat ENaC heterologously expressed in S621AENaC [S617AENaC, and αP622FENaC mutants were in pGEM-HE vector. Extension overlap PCR for site directed mutagenesis was used to generate αS617AENaC and αP622FENaC mutants. For the S617A mutation, a mutagenic forward primer with the sequence 5′-CTACGCCGGTTCCGGGCCCGGTACTGGTCTCCA-3′ and a reverse primer with the sequence 5′-TGGAGACCAGTACCGGGCCCGGAACCGGCGTAG-3′ were used to introduce a triplet mutation from CCA at nucleotides 1848–1851 to TTT. To generate αP622FENaC, a mutagenic forward primer with the sequence 5′-GCCGGTACTGGTCTTTTGGACGAGGGGCCAG-3′ and a reverse primer with the sequence 5′-CTGGCCCCTCGTCCAAAAGACCAGTACCGGC-3′ were used to introduce a triplet mutation from GGC at nucleotides 1864–1867 to AGC. Mutations were confirmed by sequence analysis. Linearized plasmids were used as templates for cRNA synthesis using T7 RNA polymerase .Full-length cDNAs for rat wild-type α-, β-, and ΓENaC  and for 621AENaC , αS617AE+ overloading [2, 0.3 Ca(NO3)2, 0.8 MgSO4, and 10 HEPES adjusted to pH = 7.4 with HCl) supplemented with 100 U/ml sodium penicillin and 100 µg/ml streptomycin sulfate. Ocytes were studied 48–72 h after injection.Isolation of oocytes was performed essentially as described previously , 32, 62.rloading , injecte2, 1 CaCl2, and 10 HEPES adjusted to pH 7.4 with Tris). In this bath solution, the pipette resistance averaged about 3 MΩ. In NaCl bath solution, NMDG-Cl was replaced by 95 mM NaCl. For continuous current recordings, the holding potential was set to − 70 mV using an EPC9 amplifier . Using a 3 M KCl flowing boundary electrode, the liquid junction (LJ) potential occurring at the pipette/NaCl bath junction was measured to be 12 mV (bath positive) [− (ECl =  − 77.4 mV) and K+ (EK  =  − 79.4 mV) under our experimental conditions. Experiments were performed at room temperature. To change from one bath solution to another, a conventional gravity-fed system controlled by a magnetic valve system (ALA BPS-8) was used in combination with a TIB14 interface . Pulse 8.78 software  was used for data acquisition. Amiloride-sensitive current (∆IAmi) in outside-out membrane patches was determined by subtracting the current value recorded in the presence of amiloride (2 μM) from the corresponding value recorded prior to its addition. The current traces were filtered at 200 Hz and sampled at 800 Hz.Current recordings from outside-out membrane patches were performed essentially as described previously , 40, 44 + content 3.2 g/kg, Cat-No 1310 from Spezialfutter GmbH & Co. KG, Lage, Germany) with free access to tap water. Isolation of renal tubules was essentially performed as described previously [For this study, we used 29 male mice  aged 6–8 weeks. Mice were bred and maintained in the animal facility of Friedrich-Alexander-Universität Erlangen Nürnberg (FAU). Mice received a standard diet : 145 Na gluconate, 5 K gluconate, 2 CaCl2, 5 barium acetate, 1 MgCl2, 3 glucose, and 5 HEPES; pH was adjusted to 7.4 with Tris. Pipette resistance measured in the bath solution was about 4–6 MΩ. Seals were formed at the apical surface of principal cells by using gentle suction. Seal resistance ranged from 3 to 10 GΩ. Series resistance was in the order of 10 to 30 MΩ and was not compensated. For continuous whole-cell as well as outside-out current recordings, the holding potential (Vhold) was set at − 60 mV. In each experiment, ∆IAmi was initially measured in the whole-cell configuration and subsequently in the outside-out configuration provided that membrane patch excision was successful. In both configurations, ∆IAmi was determined by subtracting the current measured in the presence of amiloride (2 μM) from that measured in its absence. The current traces were filtered at 250 Hz and sampled at a rate of 2 kHz. For further analysis, they were digitally re-filtered at 70 Hz. Data were analyzed using the program “Patch for Windows” written by Dr. Bernd Letz .A computer-controlled EPC-9 patch clamp amplifier  was used to perform conventional whole-cell and outside-out patch clamp recordings as previously described –59. To gper se had no detectable effect on ENaC activity in the concentrations used (data not shown). Amiloride hydrochloride was purchased from Sigma-Aldrich  and was added from an aqueous 10 mM stock solution.Recombinant constitutively active human SGK1  and recombinant active full length human DYRK2 were purchased from Biomol GmbH  as 2 μg (SGK1) and 5 μg (DYRK2) vials in 50 μl stock solution both containing as main components 50 mM Tris–HCl, 0.1 mM EGTA, 0.1% 2-mercaptoethanol, 0.15 mM NaCl, and 270 mM sucrose. SGK1 and DYRK2 pipette solutions were freshly prepared on the day of the experiment by adding stock solutions to 1 ml of the corresponding pipette solutions giving a final SGK1 and DYRK2 concentration of 80 U/ml (for experiments in oocytes) and 20 U/ml . Recombinant GSK3β and a selective GSK3β inhibitor (CHIR99021) were kindly provided by Prof. Philip Cohen . GSK3β in a concentration of 1.54 mg/ml was stored in a stock solution containing as main components 50 mM Tris–HCl, 0.1 mM EGTA, 0.1% 2-mercaptoethanol, 0.15 mM NaCl, and 50% glycerol. On the day of the experiment, the GSK3β pipette solution was freshly prepared by adding stock solution to pipette solution giving a final GSK3β concentration of 16 U/ml (for experiments in oocytes) and 8 U/ml . CHIR99021 was stored in DMSO as stock solution with a concentration of 10 mM. On the day of the experiment, stock solution was added to pipette solution giving a final CHIR99021 concentration of 2 μM [n indicates the number of individual recordings. In oocyte experiments, N indicates the number of different batches of oocytes used. In animal experiments, N is number of mice used in a set of recordings. Data from different oocyte batches and from different animals were pooled. Statistical analysis of nested experiments using N and n was not performed due to the low number of recordings obtained per animal and oocyte batch. Normal distribution of data was assessed using D’Agostino–Pearson omnibus test. Statistical significance was assessed by an appropriate parametric test: paired or unpaired Student’s t-test and Student’s ratio t-test. Significance was accepted for p < 0.05. Statistical analysis was performed using Graph Pad Prism 5.04.Data are presented as mean values ± SEM; Xenopus laevis oocytes expressing α-, β-, and γ-subunits of rat ENaC (αβγENaC). Recordings from outside-out macropatches were started about 4 min after patch excision. To minimize spontaneous channel rundown known to occur in the presence of a high extracellular Na+ concentration [+. In this solution, only a negligible inward current was detectable at a holding potential of − 70 mV. In contrast, periodic changes to NaCl bath solution revealed sizeable inward currents consistent with a current component carried by Na+ influx via ENaC. This current component was largely inhibited by the application of 2 μM amiloride, a concentration known to specifically inhibit ENaC. Using this protocol, the amiloride-sensitive sodium current (∆IAmi) was repeatedly determined to monitor ENaC activity over time. Figure Ami significantly increased by about twofold within ~ 25 min  motif has to be followed by a large hydrophobic residue to become a functional SGK1 consensus motif [P622FENaC) theoretically converts the original motif . Therefore, we asked the question whether SGK1 can activate mutant αP622FβγENaC under our experimental conditions. To address this, ENaC activity was assessed by measuring ∆IAmi in outside-out macropatches excised from oocytes expressing αβγENaC or αP622FβγENaC. In these recordings, we confirmed our previous findings [Ami remained stable over time with heat inactivated SGK1 (inactive SGK1) included in the pipette solutions  or phosphothreonine residue (PT) [Ami to less than 50% of its original value  , 24. TheS617AβγENaC. In control recordings, we demonstrated that inactive DYRK2 had no significant stimulatory effect on αS617AβγENaC  were recorded in the whole-cell and outside-out configuration of the patch-clamp technique. Microdissected and split open tubular fragments of the connecting tubule (CNT) and cortical collecting duct (CCD) were used which are known to express ENaC in principal cells. For the purpose of this study, we did not distinguish between recordings from CNT and CCD and pooled the data from all successful experiments .Our oocyte data indicate that DYRK2 and GSK3β can stimulate and inhibit ENaC activity, respectively, and that these effects are mediated by specific phosphorylation sites in the C-terminus of the channel’s α-subunit. To explore a possible regulatory role of these kinases in native renal tissue, we tested the effects of DYRK2 and GSK3β on ENaC currents in microdissected mouse distal nephron using an established experimental technique –59. TubuAmi in the whole-cell configuration, we routinely tried to excise an outside-out patch and to record from the same cell ∆IAmi also in the outside-out configuration. In successful attempts, we monitored ∆IAmi over time by repeated application and washout of amiloride  in control experiments and 193 ± 57 pA  in experiments with active DYRK2 included in the pipette solution  of the corresponding ∆IAmi determined in the whole-cell mode   in experiments with GSK3β in the pipette solution and 2.43 ± 0.45%  in control experiments with inactive GSK3β . However, ΔIAmi declined more rapidly in outside-out patches with active GSK3β in the pipette solution than in patches with inactive GSK3β  of its initial value in the experiments with active GSK3β but only to 78 ± 0.9%  in control experiments with inactive GSK3β (p = 0.02). These findings indicate that GSK3β can inhibit ENaC in native renal tubules.In similar experiments, we also tested the effect of GSK3β on ENaC in microdissected mouse distal nephron. Constitutively, active recombinant GSK3β or heat-inactivated GSK3β were added to the pipette solution. Representative traces from these experiments are depicted in Fig. K3β Fig. c. The in.49% n = ; N = 6 i.49% n = ; N = 6 i.49% n = ; N = 6 iThe key findings of the present study are the following: (i) DYRK2 stimulated and GSK3β inhibited ENaC activity in outside-out patches from oocytes; (ii) the stimulatory effect of DYRK2 depended on the amino-acid residues S621 and P622 in the C-terminus of rat αENaC which supports the hypothesis that S621 is a phosphorylation site for a proline directed kinase; (iii) the inhibitory effect of GSK3β depended on both S617 and S621, consistent with the idea that phosphorylation of S621 primes S617 to be phosphorylated by GSK3β; (iv) the S617 phosphorylation site is necessary for channel inhibition by GKS3β but not required for channel activation by DYRK2; (v) in proof-of-concept experiments we demonstrated a stimulatory effect of DYRK2 and an inhibitory effect of GSK3β on ENaC activity also in microdissected mouse distal nephron.616RSRYWS621F622). Moreover, the proline residue following S621 makes the latter an unlikely SGK1 phosphorylation site according to invitro studies [This study confirms our previous finding that in outside-out patch clamp recordings from oocytes an intact S621 phosphorylation site in the C-terminus of rat αENaC is critical for mediating acute channel activation by SGK1 included in the pipette solution . So far, studies , 85. Tak studies , 21.2+ was omitted from the pipette solution. This is consistent with the concept that an endogenous Mg2+-dependent kinase activity is present in the patch and is involved in maintaining baseline ENaC activity [We have previously shown that the stimulatory effect of SGK1 can be mimicked by including the broad range phosphatase inhibitor okadaic acid or protein phosphatase inhibitor type 2 (PIP2) in the pipette solution . Importaactivity . InclusiThe concept of an indirect effect of SGK1 on S621 is also consistent with our previous observation that plasma membrane cholesterol removal abolishes the acute stimulatory effect of SGK1 on ENaC in outside-out patches . Cholestcl1 cell line (unpublished observation). This cell line is known to express ENaC and is an established CCD model to study ENaC-mediated transepithelial sodium transport [Our findings in microdissected tubules provide proof of principle that the prototypical proline-directed kinase DYRK2 can activate ENaC not only in the oocyte expression system but also in native renal tissue. DYRK2 is known to be expressed in the kidney  includinransport , 50–52. ransport . Thus, iAt present, it is unclear how phosphorylation at S621 mechanistically causes channel activation. Our previous findings indicate that in outside-out patches, the acute stimulatory effect of SGK1 on ENaC is not due to the insertion of additional channels into the plasma membrane. Instead, constitutively active SGK1 in the pipette solution seems to activate a population of near-silent channels present in excised outside-out patches from ENaC expressing oocytes . Thus, pX. laevis oocytes and in microdissected tubules. Moreover, in the oocyte expression system, its effect depended on both S617 and on S621. In contrast, the stimulatory effect of DYRK2 was fully preserved when S617 was mutated and S621 remained intact. Thus, phosphorylation of S617 by GSK3β may serve as feedback mechanism to limit ENaC activation induced by phosphorylation of S621. Our functional data provide indirect evidence that phosphorylation of these residues is relevant for ENaC regulation. It remains a challenge for future studies to demonstrate direct phosphorylation of these sites and to elucidate how the degree of phosphorylation varies according to different physiological conditions.As stated in the introduction, DYRK2 is known to act as priming kinase for GSK3β . Our fincl1 cells using RNA-seq analysis (unpublished observation). Phosphorylation of glycogen synthase by GSK3β leads to its inactivation [GSK3β was first discovered to phosphorylate glycogen synthase, a final enzyme in the glycogen synthesis pathway. GSK3β is expressed in many tissues , 14 incltivation . Inhibittivation . Proteintivation , 67. Inttivation , 71, 77.tivation  and acuttivation . The lattivation  and the tivation  can inactivation , 34 and tivation , 79, resIn summary, our study indicates that phosphorylation of S621 by a proline-directed kinase, e.g., DYRK2, stimulates ENaC activity and primes S617 to be phosphorylated subsequently by GSK3β which limits the stimulatory effect of the initial phosphorylation and results in channel inhibition. Moreover, our findings provide proof of principle that DYRK2 and GSK3ß can activate and inhibit ENaC also in microdissected renal tubules, respectively. This supports the concept that the opposing effects of the two adjacent phosphorylation sites in the C-terminus of the channel’s α-subunit play a role in acute regulation of ENaC activity in native tissue.


West Antarctic ice-shelf thinning is primarily caused by ocean-driven basal melting. Here we assess ocean variability below Thwaites Eastern Ice Shelf (TEIS) and reveal the importance of local ocean circulation and sea-ice. Measurements obtained from two sub-ice-shelf moorings, spanning January 2020 to March 2021, show warming of the ice-shelf cavity and an increase in meltwater fraction of the upper sub-ice layer. Combined with ocean modelling results, our observations suggest that meltwater from Pine Island Ice Shelf feeds into the TEIS cavity, adding to horizontal heat transport there. We propose that a weakening of the Pine Island Bay gyre caused by prolonged sea-ice cover from April 2020 to March 2021 allowed meltwater-enriched waters to enter the TEIS cavity, which increased the temperature of the upper layer. Our study highlights the sensitivity of ocean circulation beneath ice shelves to local atmosphere-sea-ice-ocean forcing in neighbouring open oceans. A weaker ocean gyre in the Pine Island Bay, suppressed by higher sea-ice concentration over the ocean near the Thwaites Eastern Ice Shelf, allows more meltwater to enter the sub-ice-shelf cavity. This increases the ocean temperature beneath the ice. Between 1979 and 2017, Thwaites Glacier contributed 1.8 mm to global sea level, with nearly half of that contribution in the most recent decade, making Thwaites the largest net contributor to sea-level rise among Antarctic glaciers3. The eastern glacier front is buttressed by the Thwaites Eastern Ice Shelf (TEIS), which has thinned and weakened significantly in recent decades due to basal melting, mostly concentrated at the grounding zone5. High thinning rates at the grounding zone  above the deeper bathymetry areas of the shelf break, allowing it to spread over the continental shelf12. Once on the continental shelf, mCDW is topographically steered towards the ice-shelf cavities through deep troughs . An autonomous-underwater-vehicle survey below the ice-shelf front near the western side of TEIS also showed the presence of mCDW from PIB at 800–1000 m depth, indicating that there is a deep connection below TEIS through which deep warm water flows westward15. The extent of this deep connection, the pathways of the intermediate and upper ocean circulation, the driving forces, and any temporal variability of the currents under TEIS, are still unknown.The retreat of Thwaites Glacier and TEIS is sustained by ocean circulation in the Amundsen Seaghs Fig. . mCDW th17) conveys mCDW towards the Pine Island Ice Shelf (PIIS) cavity13, entraining and spreading meltwater from PIIS northwestwards18. Both the glacial meltwater component from sub-ice-shelf cavities and increasingly glacially modified mCDW are then exported westwards along the Amundsen Sea coast21. Although meltwater-enriched waters from PIIS are spread within the PIB region, it is not clear if they reach the TEIS cavity and what consequences that might have. Idealised studies suggest that the presence of lighter and fresher waters in ice-shelf cavities could increase basal melting by intensifying the horizontal circulation just beneath the ice base22. However, the effect of the interaction of exported meltwater on adjacent ice shelves is not well understood.A cyclonic gyre located in the centre of PIB  moorings were deployed through TEIS, recording temperature, salinity, pressure, and horizontal current velocity at two depths between January 2020 and March 2021  layer measured by the upper sensor of AMIGOS3c, at ~100 m beneath the ice base, showed larger interannual variability than the deeper layers . While the meltwater content in the deepest layer remained virtually constant over the 14 months, it nearly doubled in the upper layer, from ~10 g kg−1 in February 2020 to ~18 g kg−1 in March 2021 at the upper sensor of the AMIGOS3c  coupled to the AMIGOS moorings show small changes in the ice-ocean interface depth  was higher than in the deeper layers  and the flow was mostly oriented in a southwest-northeast direction , a proxy for the heat flux, delivered into the TEIS cavity by the inflow. The along-channel temperature flux in AMIGOS3c-Upper showed three peaks: July 2020, late August 2020, and February 2021, of up to ~0.2–0.4 MW m−2, which were associated with the lighter waters having higher meltwater content , the region where most meltwater is exported from beneath PIIS20, and track them forward in time. The particles initially follow the basal channels carved into PIIS and then flow westward with the coastal current . This seasonal change in the depth of the isopycnals beneath TEIS in the model is in the order of tens of metres , which we suggest prolonged the weaker PIB gyre period Fig. . The moddel Fig. , thus aldel Fig. , light  presented comparable sea-ice concentrations to January–March 2021 Fig. . Two of ods Fig. . However33. A change in the gyre direction could warm the ice-shelf cavities even faster than the simple spin-down suggested in this work because it could lift the isopycnals further up beneath the ice shelf and bring deeper warm waters upwards.Our hypothesis relies on the fact that sea-ice coverage considerably dampens the wind stress over the ocean surface. Polar ocean gyres tend to weaken during periods of extensive sea-ice coverage and less mobile sea-ice  would need to deploy sensors close to the ice base and/or use bespoke boundary-layer models to properly address these complex interactions.Theoretical and modelling studies have suggested that the addition of meltwater can lead to increased temperature and stronger baroclinic circulation beneath an ice shelf33). Gyres potentially existing in other regions around Antarctica  may cause a greater number of ice shelves to be prone to intense basal melting associated with prolonged warm conditions.The atmosphere-sea-ice-ocean interactions discussed here are important because they can prolong warm periods beneath ice shelves by allowing warm and meltwater-enriched water to enter adjacent ice-shelf cavities. The key components are: (i) gyres that respond to wind forcing adjacent to the ice shelf, and (ii) prolonged periods of landfast-ice cover damping the momentum transfer from the wind and thus spinning-down the gyre. Gyres adjacent to ice shelves are relatively small features that are still being discovered through high-resolution surveys . The AMIGOS were installed by drilling boreholes using hot water at two sites ~4.13 km apart on the Thwaites Eastern Ice Shelf: AMIGOS3c at the “basal channel site”  and AMIGOS3a at the “plateau site”   were calculated from Thermodynamic Equations of Seawater-10  Fig. . Each AM˚W) Fig. . At the -10 ref. . NeutralConductivity-temperature-depth (CTD) profiles were conducted in February and March 2020 on board RVIB Nathaniel B. Palmer using a SeaBird SBE911 + . Conductivity was calibrated using a Guideline Autosal salinometer. The CTD profiles were 1-m binned. CTD profiles from boreholes were conducted on 31 December 2019 in the AMIGOS3a site, and on 13 January 2020 in the AMIGOS3c site using the MicroCAT installed at the deeper depth for each mooring. The profiles were interpolated at 1-m intervals and smoothed with 5-m running mean.25 coupled to the AMIGOS. DTS utilizes a fibre-optic cable installed within the ice and through the ocean, and it uses Raman-backscattered photons to estimate the in situ temperature of the fibre41. The DTS interrogators  used a spatial sampling of 25 cm and were set to sample 6 times per day, except for 1 sample per day in Austral winter to conserve power. Each DTS profile uses a 1-minute integration time to improve signal-to-noise ratio. Independent temperature measurements from the MicroCATs are employed to calibrate the backscatter signal41. Calibration consisted of a simple two-point offset and gain using the MicroCATs temperature. For AMIGOS3c, the temporal Root Mean Square Error, calculated as the difference between the MicroCAT temperature and the calibrated DTS temperature at the MicroCAT depths at near coincidence times, was ~0.04 ˚C at both 316 m and 784 m. Similar Root Mean Square Errors were found for AMIGOS3a. The DTS profiles were monthly averaged for illustration purposes.In situ temperature profiles beneath the TEIS were obtained from a Distributed Temperature Sensing (DTS) and armoured fibre-optic cable similar to that previously tested on the McMurdo Ice Shelf42 were deployed in early 2019 and early 2020, respectively, in Weddell- and elephant-seals in the Amundsen Sea Embayment. All seal-tag profiles were compared with ship-based CTD measurements before deployment and the final received dataset was quality controlled using similar methods used by the Argo float community43. Spurious data were flagged and removed.Twelve and nine CTD-Satellite Relayed Data Loggers15.Temperature and salinity profiles shown in Supplementary Fig. The vertical displacement of isotherm, isohaline, and isopycnals was calculated by combining the AMIGOS timeseries measurements and the vertical borehole CTD profiles (1-m binned and then 5-m running-meaned smoothed). For each time step in the moored time series at AMIGOS3c-Upper, we determine the depth in the borehole profile that has a similar potential density to the mooring value. The vertical displacement is then the difference in depth between the mooring and the depth in the profile that has the same density. We determine this separately for potential density, absolute salinity, and conservative temperature in order to have independent time series of vertical displacements for isopycnals, isohalines, and isotherms. Because the temperature profile is not monotonic , early in the time series (up to 17th February 2020) there are two solutions for the isotherm displacement above and below the mooring depth; we show these two solutions as dots in Supplementary Fig. 24. Tracers are Θ and SA, and both are assumed to be conservative for all observations. We also assumed that the seawater in our study region is composed of the source water masses, mCDW, Winter Water, and glacial meltwater. Hence, the meltwater fraction can be derived from the observations following:−1), and Θ and SA with subscripts are endpoints of the water masses . The glacial meltwater endpoints (Θ = −90.8 °C and SA = 0 g kg−1)are consistent with Zheng et al.18 and Biddle et al.20 and do not vary over time. mCDW is the warmest water mass existing below about 400 m in our study region  from the warmest water mass measured by the deepest sensor attached on the AMIGOS system. During the study period, AMIGOS measurements showed that the mCDW properties did not change considerably . The estimated uncertainty is ±0.2 g kg−1 for the calculated meltwater content caused by measurement uncertainties. We further estimate the uncertainty induced by the Winter Water endpoint chosen. The Winter Water endpoints were set to be the surface freezing point, and the absolute salinity was set to be a value between 34.20 g kg−1 and 34.32 g kg−1. While the lower bound falls closer to the Winter Water core measured by the seal tags, the upper bound is the Winter Water value found in PIB18. Varying the Winter Water endpoints changes slightly the calculated meltwater contents, but the temporal pattern of meltwater content remains the same  for each set of MicroCAT and Aquadopp sensors is calculated using the following equation:ρ is the seawater density (kg m−3), cp is the specific heat capacity (3991.9 J kg−1 K−1), U is the along-channel velocity (m s−1) rotated 119˚ clockwise from east, Θ (K) is conservative temperature, and Θfp (K) is the conservative temperature at which seawater freezes at the surface. Positive Θflux is southwestward, i.e., into the cavity, whereas negative Θflux is northeastward, i.e., out of the cavity.Along-channel conservative temperature flux , with more accurate bathymetry for the region near Pine Island, and the Crosson and Dotson ice shelves46. The ice-shelf drafts were obtained using Antarctic Bedrock Mapping  from Nakayama et al.44, the model simulates ocean circulation in the Amundsen and Bellingshausen Seas with a nominal 3–4 km horizontal resolution on monthly averaged outputs. We use extended model simulation based on Nakayama et al.44 running from 1992 to 2020. Model bathymetry is based on the IBCSO45, with more accurate bathymetry for the region near the Crosson and Dotson ice shelves46. The ice-shelf drafts were obtained using BEDMAP-2, ref. In Nakayama et al.11 models, using Octopus (https://github.com/jinbow/Octopus). The particles are released beneath Pine Island Ice Shelf, in the area bounded by 102.073°−100.212°W and 75.355°−75.041°S  and Advanced Microwave Scanning Radiometer 2 (AMSR2) on a 3.125 km grid between 1 June 2002 and 1 April 2021 ref. . We usedSupplementary InformationPeer Review FileDescription of Additional Supplementary FilesSupplementary Movie 1


The evidence favors the latter scenario because iceberg furrows that cross cut the ridges in deep water require weakly buttressed flow as the embayment opened. In comparison with the modern grounding-zone dynamics, this paleo-perspective provides confidence in model projections that a large-scale sustained contraction of grounded ice is underway in several Pacific-Ocean sectors of the WAIS.Geological records of ice sheet collapse can provide perspective on the ongoing retreat of grounded and floating ice. An abrupt retreat of the West Antarctic Ice Sheet (WAIS) that occurred during the early deglaciation is well recorded on the eastern Ross Sea continental shelf. There, an ice shelf breakup at 12.3 ± 0.6 cal.  kyr BP caused accelerated ice-mass loss from the Bindschadler Ice Stream (BIS). The accelerated mass loss led to a significant negative mass balance that re-organized WAIS flow across the central and eastern Ross Sea. By ~ 11.5 ± 0.3 cal kyr BP, dynamic thinning of grounded ice triggered a retreat that opened a ~ 200-km grounding-line embayment on the Whales Deep Basin (WDB) middle continental shelf. Here, we reconstruct the pattern, duration and rate of retreat from a backstepping succession of small-scale grounding-zone ridges that formed on the embayment’s eastern flank. We used two end-member paleo-sediment fluxes, i.e., accumulation rates, to convert the cumulative sediment volumes of the ridge field to elapsed time for measured distances of grounding-line retreat. The end-members fluxes correspond to deposition rates for buttressed and unbuttressed ice stream flow. Both scenarios require sustained rapid retreat that exceeded several centuries. Grounding-line retreat is estimated to have averaged between ~ 100 ± 32 and ~ 700 ± 79 ma This raises concern that an unstable collapse may be underway4. The term collapse is not precisely defined but is generally used to describe a significant contraction in the extent and volume of grounded ice within a relatively short time. In the Bellingshausen-Sea sector, 65% of WAIS grounding lines have retreated between 1990 and 20155. These dynamics are at least partly driven by upwelled circumpolar deep water that advects onto the continental shelf and melts the ice sheet’s marine margins. Since 1979, discharge from fast-flowing WAIS glacial systems has contributed nearly 7 mm of sea-level equivalent volume to global sea level rise6. Recent modeling studies have projected that Pine Island Glacier losses could exceed 100 Gt/yr−1 within 20 years3. Model simulations project that a transition to an even more rapid retreat could occur within 200–900 years2. These projections all rely on two tacit assumptions: firstly, that the current rapid contractions are anomalously fast and secondly, that the fast rates will be sustained for several centuries. The assumptions are important to justify because changes to these large-scale glacial systems are probably complex and some studies have shown that feedbacks such as isostatic rebound7, grounding zone sedimentation8 or sea-level fall9 may halt and/or even reverse rapid flow and retreat.Glaciers in the Amundsen Sea sector of West Antarctica are speeding up and grounding lines retreating as their ice shelves thin10. The relative shortness of the satellite-era observations highlights the need to assess longer-term dynamics associated with past episodes of major ice sheet contraction. Previous studies of the Antarctic continental margin glacial morphology and sedimentology have estimated that the post-LGM retreat rates ranged between 40 and 180 ma−113. Here, we evaluated a post-LGM record from the eastern Ross Sea continental shelf where several details of WAIS retreat are better constrained in the WDB. There, previous studies have demonstrated that the paleo-BIS experienced an abrupt retreat of ~ 200 km from an outer to a middle continental shelf grounding-line stillstand position  all of which were more than 20 m thick8. The combined overlapping aggradational stack of GZWs constructed the bathymetric saddle  position at the continental shelf edge prior to 14.7 ± 0.4 cal kyr BP8 m3 a−1 but the flux increased nearly sevenfold from 670 ± 2.0 × 107 to 4.7 ± 1.0 × 108 m3 a−1 following the ice shelf break up at 12.3 ± 0.6 cal kyr BP15. Despite ice shelf breakup, the paleo-BIS maintained its outer-continental shelf position due to the stabilizing effects of grounding-zone wedge sediment aggradation.Isopach mapping of the stillstand GZWs and chronologic control indicate that the paleo-sediment flux of BIS averaged 1.7 × 103 a−1) and produced several centuries of a mass imbalance of − 45.4 ± 34 km3 a−1, equivalent to a basin-wide thinning rate of − 0.2 ± 0.14 ma−115. Ice volume discharge exceeded the balance velocity by a factor of two and implies ice mass imbalance of − 40 Gt a−1 for several centuries, which eventually triggered rapid grounding line retreat at ~ 11.5 ± 0.3 cal kyr BP.During the final stages of the stillstand, the ice-volume discharge exceeded the estimated average accumulation  between the seafloor and the basal reflector on six cross sections oriented approximately perpendicular to the ridge crests  in the Glomar Challenger and Little America basins that converge towards the WDB middle continental shelf , then the embayment opened in ~ 280 years.Sediment supply to the embayment’s eastern flank was probably derived from the MacAyeal Ice Stream (MIS) flowing through LAB2. It is important to recognize that the modern-day retreat of ice streams have oscillated between both faster and slower rates in time and space36. During the past four decades, several large ice streams in West Antarctica have exhibited rates that exceeded even the upper-end paleo-retreat rate estimate. For example, Pine Island Glacier retreated at ~ 1000 ma−1 for nearly a decade between 1992 and 201137 but then retreat rate substantially decreased10. Likewise, in the Bellingshausen and Amundsen Sea sectors, several grounding zones experienced localized rapid retreat at rates ranging up to 1200 ma-1 between 2010 and 2016 whereas broader areas of the same regions have retreated at slower rates ranging from 100 to 300 ma−110. Between 1990 and 2015, retreat in the Bellingshausen sector proceeded with maximum rates of ~ 200 ma−1 whereas adjoining drainage areas in the Amundsen-Sea sector  experienced faster retreat5. In the largest catchment of the Amundsen Sea sector, the retreat of the Thwaites Glacier increased to 420 ma−1 by 201610. The opening of the WDB embayment may have also proceeded with similar oscillations like those observed for modern ice streams. Taken at face value, the decreased thickness of the younger ridges suggests that the retreat rate increased by ~ 70% from ~ 515 to ~ 880 ma−1 for that part of the embayment’s eastern flank surveyed  interpolation within QGIS 3.18 creating a final DEM of the basal surface. Cross-sections were generated using the Line Interpretation Tool in the 3D Analysis Toolbox 7 on a common vertical and horizontal scale.A basal reflector observed to underlie part of the surveyed area on CHIRP data was correlated and mapped in Petrel 18.1. An initial subsurface map of the basal reflector was converted to meters depth below sea level with a velocity of 1650 msIn QGIS 3.18, we clipped the seafloor DEM to the extent of the basal reflector DEM so that Raster calculations could be computed to the edges of that data set. The clipped seafloor DEM was subtracted from the basal reflector DEM to create an isopach of positive height between the basal reflector and seafloor.Cross-sections across the isopach have x values corresponding to distance and y-values corresponding to height of sediment above the basal surface. The y-positions  were multiplied by the individual spacing between x positions and the areas were summed to estimate cross-sectional area of the ridge field moraines. We converted the cross-sectional areas to a stream-wise volume by multiplying the cross-section area by 1 m of the paleo-grounding line length measured perpendicular to the ridge crest.15 (2020) to a stream-wise quantity (in m3/m/a) by dividing their 3D flux value by 100,000 m . The lower-end sediment flux (670 ± 20 m3/m/a) corresponds to the average rate of grounding-zone deposition prior to ice shelf breakup . The upper-end sediment flux (4700 ± 100 m3/m/a) corresponds to the average rate sediment after the ice-shelf breakup . We used the stream-wise fluxes to estimate the elapsed time to deposit the morainal ridges along cross sections. The time elapsed to deposit the ridges is the quotient of a cross-section’s cumulative sediment volume and the paleo-BIS stream-wise sediment flux. We then estimated the grounding-line retreat rate by dividing the cross-section distance (from the oldest to the youngest ridge) by the time elapsed to deposit the ridges.We converted the lower- and upper-end BIS paleo sediment fluxes from Bart and TulaczykSupplementary Information.


ALAS is evolutionarily related to transaminases and is therefore classified as a fold type I PLP-dependent enzyme. As an enzyme controlling the key committed and rate-determining step of a crucial biochemical pathway ALAS is ideally positioned to be subject to allosteric feedback inhibition. Extensive kinetic and mutational studies demonstrated that the overall enzyme reaction is limited by subtle conformational changes of a hairpin loop gating the active site. These findings, coupled with structural information, facilitated early prediction of allosteric regulation of activity via an extended C-terminal tail unique to eukaryotic forms of the enzyme. This prediction was subsequently supported by the discoveries that mutations in the extended C-terminus of the erythroid ALAS isoform (ALAS2) cause a metabolic disorder known as X-linked protoporphyria not by diminishing activity, but by enhancing it. Furthermore, kinetic, structural, and molecular modeling studies demonstrated that the extended C-terminal tail controls the catalytic rate by modulating conformational flexibility of the active site loop. However, the precise identity of any such molecule remains to be defined. Here we discuss the most plausible allosteric regulators of ALAS activity based on divergences in AlphaFold-predicted ALAS structures and suggest how the mystery of the mechanism whereby the extended C-terminus of mammalian ALASs allosterically controls the rate of porphyrin biosynthesis might be unraveled. PyridoxALAS1, which acts as a “housekeeping” gene and initiates heme biosynthesis in all cells for production of cytochromes and other heme-binding proteins, and ALAS2, which is expressed only in developing erythrocytes and produces, almost exclusively, the much larger quantities of heme required for hemoglobin formation , consensus sequences containing a cysteine-proline dipeptide with the cysteine functioning as a ligand to Fe3+-heme   HRMs 4 and/or 5 facilitate feedback inhibition of ALAS1; 2) under oxidizing conditions, the CXXC motif forms a disulfide bond that causes the C-terminal extension to fold over HRMs 4 and 5 such that it sterically prevents hemin binding and feedback inhibition; 3) under non-oxidizing conditions, the CXXC motif is reduced and adopts an alternative conformation wherein HRMs 4 and 5 are exposed to provide feedback inhibition by excess heme. Stated more concisely, feedback inhibition of ALAS1 by heme is dependent upon cellular redox status.Based on the alignment of the ALAS2 structures we put forth the following postulates: 1) the C-terminal extension of ALAS2 adopts two different conformations, neither of which prevents feedback regulation via heme binding to HRMs 4 and 5. 2) In ALAS2 oxidizing conditions cause disulfide bond formation in the CXXC motif and movement of the extended C-terminus not over HRMs 4&5 but instead to a more equatorial and activated position relative to the enzyme, thereby relieving the autoinhibition observed when the extended C-terminus folds over the active site. Stated more succinctly, heme and redox status independently regulate ALAS2 activity.These postulates are not incompatible with the possibility of protein-protein interactions regulating activity. Of course, experimental data will be required to further support or refine the views presented here, but whatever the outcome the remarkably divergent structures discussed here will likely represent a key test of the capacity of AlphaFold to discern fine structural differences and facilitate prediction of allostery in all enzymes, including those dependent upon PLP for functionality.


Arctic sea ice retreat is linked to extrapolar thermal energy import, while the potential impact of pan-Arctic river heat discharge on sea-ice loss has been unresolved. We reconstructed the Holocene history of Arctic sea ice and Russian pan-Arctic river heat discharge, combining ice-rafted debris records and sedimentation rates from the East Siberian Arctic Shelf with a compilation of published paleoclimate and observational data. In the mid-Holocene, the early summer (June–July) solar insolation was higher than that during the late Holocene, which led to a larger heat discharge of the Russian pan-Arctic rivers and contributed to more Arctic sea ice retreat. This intensified decline of early-summer sea ice accelerated the melting of sea ice throughout the summertime by lowering regional albedos. Our findings highlight the important impact of the larger heat discharge of pan-Arctic rivers, which can reinforce Arctic sea-ice loss in the summer in the context of global warming. Based on marine multiproxy records, a new study outlines the role of larger heat discharge of the pan-Arctic Rivers in determining the pronounced sea ice retreat over the East Siberian Arctic Shelf in the mid-Holocene. However, future climate trends in association with sea ice melting remain elusive due to an insufficient understanding of the mechanism of retreat or even the absence of summer Arctic sea ice in the future. By referring to the Arctic climate of warmer intervals in the past, paleoclimate studies can provide clues for the future; e.g., the mid-Holocene (MH) was the most recent warmer climate interval relative to modern conditions.Arctic sea ice has dramatically declined under global warming, with feedback accelerating ongoing warming conditions6, poleward moisture in association with latent heat transport7, and the Atlantic9 and Pacific inflows10 of relatively warm water  of the annual suspended sediment is discharged from rivers into the ESAS during the early summer when the solar insolation is at a maximum27, directly depending on both freshwater temperatures 29 and river runoff amounts 32. Since the pan-Arctic river thermal flux is jointly determined by river runoff and freshwater temperature15  is a prominent area of increasing sea ice seasonality, with nearly sea ice-free conditions in summer in contrast with complete sea ice coverage in winterr24 Fig.  and is t35, and the sedimentation rate to reconstruct the Holocene variations in Arctic sea ice and regional river heat discharge, respectively  dates and optically stimulated luminescence (OSL) ages of quartz after the application of polynomial analysis to assess the correlation of dating data between radiocarbon and OSL quartz ages and then the recalibration of OSL age data , known as the ice-rafted debris (IRD) proxy μm, %, k 36 Fig. . Because 36 Fig. , this foOur measurements of marine proxies, together with the compilation of a published dataset for the sedimentation rate, sea ice, inland permafrost, basin surface air temperature, and precipitation, as well as observation data, reveal the coherent occurrences of the loss of Arctic sea ice and larger river heat discharges in the MH compared to the LH Figs.  and 3. T37 and Fram Strait38, suggesting that the IRD was mainly governed by sea ice export from the ESAS. In contrast, the dinocyst-based reconstruction of sea ice in the marginal seas of Alaska has revealed a longer sea ice cover during the MH compared to the LH40. This result indicates that the external western Arctic sea ice could not influence the IRD records in the ESAS region, although it was transported by the Beaufort Gyre. Thus, all these IRD records indicate that the ESAS sea ice has continuously developed since the MH. Moreover, regional sea ice biomarker values gradually increased from the MH to the LH  record characterizes an increasing tendency from the MH to the LH Fig. . The rel LH Fig. , suggest34 and Holocene carbon isotopes and terrigenous biomarkers43 also indicate that the sediment source in the shelf area was mainly the Siberian rivers, which coincides with the observation that the modern surface open water environment is dominated by river runoff , while it is asynchronous with the late summer (August) solar insolation evolution with a maximum at ~5.0 ka51 Fig. . This fi MH Fig. . At this13 and then drives the maximum open sea surface temperature to exceed 8 °C in mid-June12 and 12 °C at the beginning of July11. As a positive feedback mechanism in response to the enhanced river heat input during the MH, the significant loss of Arctic sea ice along with sediment- and phytoplankton-rich freshwater could have prominently reduced the early summer sea ice albedo during the MH  was set as 53 ± 67 years, which was calculated based on five age points collected in the Laptev Sea63. Between two adjacent calendar age points, the interpolated ages and 2-sigma uncertainties were calculated using the Clam age-depth estimate program 2.2 via open-source R statistical software64. Additionally, all the age-depth models of the referenced ESAS sediment cores based on the 14C dating analyses of shells were recalibrated using the same dataset and statistical method to compare the various proxies.The age model of sediment core LV77-36-1 is based on twelve accelerator mass spectrometry 66 was not abundant enough to be analyzed during this interglacial period, the quartz samples in the 4–11 μm fraction67, which were referenced by the grain-size distributions  were used to obtain the OSL dating samples, which were then immediately sealed with covers and black tape and wrapped with an opaque plastic bag to avoid light exposure. The samples were pretreated and measured in the optical dating laboratory with red LED illumination at the Qinghai Institute of Salt Lakes, Chinese Academy of Sciences (Xining). Because the sufficiently bleached quartz in the ≥63 μm fraction during sea ice transport43, the sedimentary processes from the source to the sink can prevent quartz from being exposed to light. First, inland East Siberia (sediment source region) has been covered with permafrost and land snow/ice for the long term70. Second, a large mass of sediment due to river erosion is rapidly transported into the marginal seas in certain months (mainly in June and July32), resulting in high sedimentation rates on the ESAS71. Hence, the older age estimations by OSL dating were observed along with the higher sedimentation rate during the Holocene 72, particularly in the MH  and 75.4 cm/ka (core LV77-41-1) during the MH (7.5–4.0 ka), which contrasts with values of 22.7 cm/ka (core LV77-36-1) and 36.7 cm/ka (core LV77-41-1) during the LH , 299 samples in total were collected at 2-cm intervals after being described and photographed. Before the instrument mensuration, each bulk sample was pretreated with hydrogen peroxide  for 24 h at 20 °C and then placed in a thermostat water bath (85 °C) for 2 h. This process was repeated thrice to remove all organic matter. After removing the biogenic carbonate fraction by pretreating it with hydrochloric acid  for 24 h at 20 °C, the detrital sediment and biogenic silica were isolated. Subsequently, these residual samples were rinsed with distilled water (3×) to make the PH values of the solution equal to ~7. The samples were then treated with sodium carbonate solution  for 4 h at 85 °C in a thermostat water bath to remove the fraction of biogenic silica. Later, the residual materials were rinsed with distilled water (3×) to reduce the influence of reagents; then, potential aggregates of samples were disaggregated using an ultrasonic cleaner for 1 min. Finally, grain-size measurements were immediately performed in deionized and degassed water to avoid gaseous influence. Each measurement was repeated twice to ensure that the results were repeatable  of the bulk samples were performed using a Thermal iCAP RQ ICP–MS system , while the station-based data of Russian pan-Arctic river runoff and freshwater temperature were from R-ArcticNet (www.r-arcticnet.sr.unh.edu/). The data for the ESAS  and pan-Arctic  surface air temperature anomalies, as well as the Siberian River basin  precipitation, were regional average values. The river water discharge data were summed, while the river freshwater temperature (May 5–June 5) data were averaged for the Yenisey, Lena, Yana, Indigirka, and Kolyma Rivers. These representative river basins are located in Siberia (85–180°E), and they are nearly completely covered by permafrost14. The datasets for the gauging stations included Igarka (Yenisey River), Kusur (Lena River), Ubileynaya and Djahgky (Yana River), Vorontsovo (Indigirka River), and Kolymskoye and Srednekolymsk (Kolyma River). The river runoff datasets for the Yenisey, Lena, and Indigirka Rivers were complete from A.D. 1938 to 1994. Values for the Yana River between A.D. 1972 and 1989 were averaged between datasets from the Ubileynaya (dataset from A.D. 1972 to 1994) and Djahgky (dataset from A.D. 1938 to 1989) gauging stations because they are adjacent. Values for the Kolyma River at the Kolymskoye gauging station (dataset from A.D. 1978 to 1994) from 1938 to 1977 were derived from the next upstream gauging station at Srednekolymsk (dataset from A.D. 1938 to 1988)79, according to the linear equation79 between these stations for an overlapping period of 11 years . Because the NCEP reanalysis datasets of the surface air temperature were complete from A.D. 1948 to the present, the overlapping period (A.D. 1948–1994) of river runoff, water temperature, and air temperature was analyzed in this study.Previous studies have suggested that recent global warming has caused the daily maximum discharge to occur earlier in spring (from June to late May)Supplementary InformationPeer Review File


Cyclopoida and 15 species of Siphonostomatoida, are reported from Korean waters, which were collected using underwater light traps at 33 collection sites around the South Korean coast. Ten new species are described: Hemicyclopsrapaxsp. nov. in the family Clausidiidae; Pontoclausiacochleatasp. nov. and P.pristinasp. nov. in the family Clausiidae; Heteranthessiusunisetatussp. nov. in the family Lichomolgidae; Pusanomyicolasensitivusgen. nov., sp. nov. in the family Myicolidae; Polyankylisbogilensissp. nov. in the family Polyankyliidae; Pseudanthessiuslinguifersp. nov. in the Pseudanthessiidae; Eupolymniphilusfoliatussp. nov. in the family Sabelliphilidae; and Acontiophorusestivalissp. nov. and Thermocherespacificussp. nov. in the family Asterocheridae. Supplementary descriptions or notes for other species are provided as appropriate.Thirty-nine species of symbiotic copepods, comprising 24 species of poecilostome  Light traps are useful tools for collecting marine animals. According to Anchistrotoslucipetus as a new species that was collected using a light trap in Irish waters, indicating that strict parasitic animals can be caught in light traps.Crustaceans are the most abundant marine animals that are caught in light traps . McLeod Cyclopoida and Siphonostomatoida) are recorded in the present paper.Recently copepods caught in light traps have been recorded frequently in Korea , 2019. TMABIK), Seocheon, Korea. Scientific names were checked against those in WoRMS . The copepod is presumed to have escaped from its bivalve host in a fish market aquarium into the adjacent waters of the collection site, where the host cannot dwell due to the water pollution.This copepod has been known only from the bivalve Taxon classificationAnimaliaCyclopoidaAnthessiidaeDo & Kajihara, 198493A11998-D7D0-5DEF-94BA-14A6B137FF0DTwenty ♀♀, 9 ♂♂, Site 4, 19 Jul. 2016; 2 ♀♀, Site 5, 21 Jul. 2016; 37 ♀♀, 2 ♂♂, Site 7, 21 Jun. 2019; 7 ♀♀, 3 ♂♂, Site 8, 18 May 2015; 17♀♀, 2 ♂♂, Site 9, 17 May 2015; 8 ♀♀, 2 ♂♂, Site 11, 03 Jun. 2019; 1♀, 1 ♂, Site 11, 07 Jul. 2020; 9 ♀♀, Site 11, 16 Apr. 2014; 10 ♀♀, Site 11, 20 Aug. 2020; 11 ♀♀, Site 12, 16 Mar. 2013; 1♀, 1 ♂, Site 13, 03 Jul. 2020; 9 ♀♀, 1 ♂, Site 14, 03 Jul. 2020; 1 ♀, Site 15, 04 Jul. 2020; 6 ♀♀, Site 16, 04 Jul. 2020; 5 ♀♀, Site 17, 13 May 2015; 24 ♀♀, 4 ♂♂, Site 18, 27 Apr. 2017; 2 ♀♀, Site 19, 05 Jun. 2020; 6 ♀♀, 2 ♂♂, Site 21, 26 May 2017; 62 ♀♀, 13 ♂♂, Site 22, 26 Apr. 2021; 30 ♀♀, 10 ♂♂, Site 22, 31 May 2021; 11 ♀♀, 3 ♂♂, Site 23, 24 Apr. 2021; 3 ♀♀, 1 ♂, Site 26, 06 Jul. 2016; 10 ♀♀, 1 ♂, Site 32, 24 May 2020; 4 ♀♀, 2 ♂♂, Site 33, 11 Aug. 2020.Body Fig.  narrow. Mandible Fig.  with bifLeg 4 with three spines and five setae on third exopodal segment. Leg 5 exopod 2.1 × longer than wide.Male. Body form as in female. Body length of measured specimen 1.20 mm.Anthessiusgraciliunguis Do & Kajihara, 1984 was described originally as an associate of the mussel Mytilusgalloprovincialis Lamarck, 1819 from Japan , Pectenalbicans , Scaeochlamyssquamata , and Solecurtusdivaricatus  in Korea. M.galloprovincialis for copepods, this mussel seems to be the major host of A.graciliunguis, considering that only this mussel inhabits all of those 19 collection sites.om Japan . Kim  the caudal ramus is ~ 3.5 × longer than wide, (2) the terminal segment of antenna is 3.0 × longer than wide; (3) the convex outer margin of the distal lash of maxilla is ornamented with five spines; (4) the third exopodal segment of leg 4 is armed with three spines and five setae; and (5) the exopod of leg 5 is 2.1 × longer than wide. The first (1) and last (5) may be the simple combination of features sufficient to differentiate A.graciliunguis from its congeners.The diagnostic morphological features of the female of Taxon classificationAnimaliaCyclopoidaClausidiidaeTanaka, 1961CA383165-3A09-57F5-BA01-4CFDE1E94A0FOne ♂, Site 4, 19 Jul. 2016; 1 ♀, Site 12, 16 Mar. 2013; 1 ♀, Site 33, 11 Aug. 2020.Conchyliurusquintus is widely distributed along the entire coast. It has a low host specificity, inhabiting 12 species of bivalves in Korea . Antennule with same armature formula as in female. Antenna, mandible, maxillule the same as those of female. Basis  of maxilla terminating in stout claw. Maxilliped four-segmented; first segment (syncoxa) with single large spinulose seta subdistally on inner margin; second segment (basis) broadened proximally, markedly tapering distally, armed with two unequal setae (one spinulose and one minute), and ornamented with three longitudinal rows of denticles along inner margin; small third segment  unarmed; terminal segment forming long, curved claw bearing two setae proximally.Leg 1 different from that of female in absence of inner distal spine on basis. Legs 2–4 as in female. Leg 5 consisting of single dorsolateral seta on fifth pedigerous somite and exopod; protopod completely fused with somite. Leg 6 represented by one spine on posterolateral corner of genital operculum.Taxon classificationAnimaliaCyclopoidaClausidiidae23EAFB58-675D-59A0-BCE5-8CA97449FDF7https://zoobank.org/9FE3EF15-2C7B-4266-B619-190EAEE13FC8Holotype ♀ (MABIK CR00250118) and paratype ♀ (MABIK CR00250119) preserved in 90% alcohol, Site 22 , 31 May 2021, leg. J. Lee; paratype ♂  dissected and mounted on a slide, Site 22, 26 April 2021, leg. J. Lee and C. Y. Chang; 1 ♀ preserved in 90% alcohol and 1 ♀ (figured) dissected and mounted on a slide, Site 11 , 07 Jul. 2020, leg. J. G. Kim.Female. Body . Antenna, labrum, mandible, paragnath, maxillule as in female. Maxilla different from that of female; basis armed with two spines and one seta and terminating in stout, claw-like process bearing spinules on outer margin and granule-like papillae on distal region Fig. . MaxilliLeg 1 different from that of female in absence of inner distal element on basis Fig. . Legs 2–rapax is derived from the Latin rapa (grasping), alluding to the grasping form of the female maxilliped.The specific name Hemicyclopsrapax sp. nov. is characterized by its peculiar female maxilliped, in which the terminal segment is transformed to a large hook, as in the males of existing species. This form of female maxilliped is very unusual for the genus, since the terminal segment  of the female maxilliped in other species of the genus generally terminates in a spiniform process (or a spine). The only other example of this peculiar female maxilliped in Hemicyclops is that of H.cylindraceus , as illustrated by H.cylindraceus differs from H.rapax sp. nov. in having a narrow, almost cylindrical body, five setae on the first antennular segment, four setae (without spines) on the exopod of leg 5, and an inner distal element on the basis of leg 1 , the genital double-somite of the female is distinctly longer than wide (more than 1.2 × longer than wide); in H.tamilensis  the urosome of the female is six-segmented and the exopod of leg 5 is elongated; in H.saxatilis Ho & Kim, 1992 the basis of male leg 1 bears an inner distal spine, the first segment of the male maxilliped is armed with two (rather than one) setae, and the maxilla is not sexually dimorphic. In the remaining species, H.leggii  described based on the male, the third endopodal segment is armed with five armature elements , the basis of male leg 1 is armed with an inner distal spine, and the first segment of male maxilliped is armed with two setae. These differences are considered sufficient to distinguish the new species from these eight congeners.Taxon classificationAnimaliaCyclopoidaClausidiidaeMoon & Kim, 2010FA51A4C1-C5D2-5B62-A67C-519676627FD8Two ♀♀, Site 11, 20 Aug. 2020; 1 ♀, Site 12, 16 Mar. 2013; 2 ♀♀, 1 ♂, Site 15, 04 Jul. 2020; 1 ♀, Site 20, 05 Jun. 2020; 2 ♀♀, 8 ♂♂, Site 26, 06 Jul. 2016; 1 ♂, Site 33, 11 Aug. 2020.H.gomsoensis Ho & Kim, 1992, H.parilis from burrows of unknown invertebrates on the south coast of Korea. The host of this copepod has turned out to be the decapod crustacean Upogebiaissaeffi . We collected it at six collection sites in this study, which indicates that the decapod host is likely to occur at those sites.Due to the close relatedness of this species to Taxon classificationAnimaliaCyclopoidaClausidiidaeKim & Stock, 1996B3028D0B-8E5F-52A0-80F5-93B942E75659One ♀, Site 1, 28 Jun. 2021; 1 ♀, Site 22, 31 May 2021.Hersiliodesexiguus which was originally recorded as an associate of the clam Ruditapesphilippinarum  inhabiting a brackish lagoon on the east coast of Korea  dissected and mounted on a slide, Site 22 , 26 Apr. 2021, leg. J. Lee and C. Y. Chang; Paratype ♂ (MABIK CR00250125) dissected and mounted on a slide, Site 27 , 09 Jul. 2016, leg. J. Lee and C. Y. Chang.Female. Body , alluding to the spoon-like mandible of the new species.The specific name Pontoclausia which contains five known species (Pontoclausiacochleata sp. nov. may be clearly defined from other species by its three unique features: (1) the mandible is unarmed, with a scoop-like distal part, rather than armed with one or two armature elements as in congeners; (2) the maxilliped is unsegmented and tipped with one seta, rather than segmented and unarmed as in congeners; and (3) the third exopodal segment of leg 1 is armed with eight armature elements , rather than six or seven elements as in congeners. It is remarkable that the form of the mandible of the new species is very unusual for the Clausiidae. Nevertheless, we have refrained from establishing a new genus, since other features of mouthparts and legs are as usual for the genera within Clausiidae.With the three-segmented rami of legs 1–4, the inner distal spine on the basis of leg 1, and the laterally positioned leg 5, the new species apparently belongs to the genus  species . Within Taxon classificationAnimaliaCyclopoidaClausiidae0DB635BF-C436-51D7-9368-882771737A18https://zoobank.org/EBD91A7F-FD84-4B52-BD6A-590BAB4C21B8Holotype ♂ (MABIK CR00250126) dissected and mounted on a slide, Site 1 , 28 Jun. 2021, leg. J. G. Kim.Male. Body , referring to the primitive condition of its antenna and mouthparts.The specific name of the new species is derived from the Latin Pontoclausiapristina sp. nov., it is distinctively characterized by its primitive antenna which is four-segmented with a full armature and by primitive, Hemicyclops-type mandible, maxillule and maxilla. The taxonomic position of the new species appears to be intermediate between the genera Hemicyclops and Pontoclausia of the Clausiidae. In the new species (1) the body is slender, harpacticiform (Pontoclausia-type feature); (2) the antennule is six-segmented (Pontoclausia-type); (3) the antenna is four-segmented, with 1, 1, 4, and 7 armature elements respectively on the first to fourth segments (Hemicyclops-type); (4) the mandible bears three or four distal armature elements (Hemicyclops-type); (5) the maxillule is distally bilobed with a total of eight setae (Hemicyclops-type); (6) the maxilla is two-segmented, with two distinct setae on the proximal segment and three armature elements plus one spiniform process on the distal segment (Hemicyclops-type); (7) the endopod of male leg 1 is two-segmented (Pontoclausia-type); (8) most of swimming legs lack the inner coxal seta (Pontoclausia-type); (9) the second endopodal segment of legs 2–4 bears only a single inner seta (Pontoclausia-type); and (10) the setation of the third exopodal and endopodal segments of most swimming legs is reduced (Pontoclausia-type). We consider that the two-segmented condition of the endopod of male leg 2 (above character state 7), which is a consistent, typical feature of Pontoclausia, is the most important taxonomic feature for determining the familial position of the new species; therefore, we place it within the Clausiidae. Pontoclausiapristina sp. nov. is distinguished from its congeners and other species in the family by the above Hemicyclops-type features.Although only a single male specimen is available for the description of Taxon classificationAnimaliaCyclopoidaKelleriidaeSewell, 1949D7A79AC9-F083-52BF-9998-DAEF2D97B64COne ♀, Site 15, 04 Jul. 2020.K.grandisetiger Kim, 2006 with K.andamanensis Sewell and redescribed it.Taxon classificationAnimaliaCyclopoidaLichomolgidaeAvdeev, 19878807C2BA-7FC0-5DE0-9F55-002B8EB51B5EOne ♀, Site 12, 16 Mar. 2013.Herrmannelladentata was originally described as an associate of the bivalves Myajaponica Jay, 1857 and Garikazusensis  in the Peter the Great Bay, Russia  on the south coast., Russia . In KoreTaxon classificationAnimaliaCyclopoidaLichomolgidaeKim I.H., 19921003988B-9B39-5160-90E5-3D5A846A347DOne ♂, Site 11, 03 Jun. 2019; 1 ♀, 4 ♂♂, Site 12, 16 Mar. 2013; 1 ♂, Site 17, 13 May 2015.Saxidomuspurpurata .This copepod species had been found only in the bivalve Taxon classificationAnimaliaCyclopoidaLichomolgidaeKim I.H. & Sato, 20106F515870-D939-56D5-AA5C-34C6F663A439One ♀, 3 ♂♂, Site 33, 11 Aug. 2020.Herrmannellamacomae from the clam Limecolacontabulata  (recorded as Macomacontabulata) in Mutsu Bay, Japan. This copepod is new to the Yellow Sea, Korea and this is only the second record of the species.Taxon classificationAnimaliaCyclopoidaLichomolgidae74243762-19C3-5936-90DE-FB617AC12F2Ahttps://zoobank.org/E7E5EAEE-6742-4312-8467-11EA6CF572F3Holotype ♂ (MABIK CR00250127) dissected and mounted on a slide, Site 6 , 21 Sep. 2020, leg. J. Lee and J. G. Kim.Male. Body  from an unknown host in Scotland , the major host.Taxon classificationAnimaliaCyclopoidaMyicolidae019E2CE3-04C5-51F3-A795-4D0D711F9929https://zoobank.org/D280A953-BE0A-458B-A438-650794FC0354Male. Body narrow, cyclopiform, clearly segmented. Prosome consisting of cephalosome and four pedigerous somites. Urosome six-segmented. Caudal ramus with six setae, Antennule seven-segmented, heavily armed with setae and aesthetascs; first and second segments with multiple aesthetascs. Antenna three-segmented, consisting of coxobasis and two-segmented endopod, and terminated in single, strong claw. Labrum broader than long, with short posterolateral lobes. Mandible distally armed with three denticle-like elements, innermost one articulate at base. Maxillule as lobe tipped with two setae. Maxilla as lobe tipped with single seta. Maxilliped four-segmented; armature formula 0, 2, 0, and 1; terminal claw reduced, rudimentary. Legs 1–4 biramous, with three-segmented rami. Coxa of all swimming legs with small inner seta. Leg 1 lacking inner distal armature element on basis. Second endopodal segment of legs 2–4 armed with two inner setae. Third endopodal segment of legs 2 and 3 armed with three spines plus three setae . Third exopodal segment of legs 3 and 4 armed with three spines plus five setae . Leg 5 consisting of protopod and exopod; protopod well-defined from somite; exopod armed with three setae. Leg 6 represented by three setae on genital operculum.Pusanomyicolasensitivus gen. nov., sp. nov. .Myicola, the type genus of the family. Gender masculine.The generic name is the combination of “Pusan”, the type locality of the type species, and Myicolidae, including the highly transformed genus Crucisoma Kabata, 1981. While establishing the family Anthessiidae, Conchocheres Sars, 1918 from this family due to the lack of long elements on the mandible, the absence of the maxilliped in the female, and the presence of three setae only on the exopod of leg 5, but he did not determine the familial position of Conchocheres. Conchocheres in the Myicolidae on the basis of similarities in the armature of the antenna and in the form of the caudal rami, but they mentioned that the genus differed from all myicolids in the absence of the inner seta on the basis of leg 1, a characteristic found in the Anthessiidae.Anthessiidae is in the antennule. In poecilostome cyclopods, the armature of three terminal segments of the antennule  is generally determined as early as the copepodid II stage, and this armature formula remains unchanged throughout subsequent developmental stages. However, the position of the aesthetasc on the antepenultimate segment (the segment of 4+aesthetasc) differs between the Anthessiidae and other poecilostome families, since the aesthetasc in the Anthessiidae is inserted at the distal corner, accompanied with anterodistal seta  the male urosome is five-segmented in Conchocheresmalleolatus Sars, 1918, the type and only species of Conchocheres, while it is six-segmented in Pusanomyicolasensitivus gen. nov., sp. nov.; (2) the male antennule of C.malleolatus bears five aesthetascs as illustrated by P.sensitivus gen. nov., sp. nov.; (3) the male maxilliped of C.malleolatus bears a large terminal hook, while it is markedly reduced in P.sensitivus gen. nov., sp. nov.; (4) the third exopodal segment of leg 1 is armed with three spines plus four setae  in C.malleolatus, but with four spines plus four setae  in P.sensitivus gen. nov., sp. nov.; and (5) the third endopodal segment of leg 4 is armed with one spine plus three setae  in C.malleolatus, but with three spines plus two setae  in P.sensitivus gen. nov., sp. nov.Pusanomyicola gen. nov. in the Myicolidae on the basis of its myicolid form of antenna bearing a single robust terminal claw and a truncate inner distal seta on the terminal segment, the presence of a group of spinules on the labrum, maxilla and genital operculum, and the myicolid form mandible. We confirm that Conchocheres, which shares important character states with Pusanomyicola gen. nov., is placed in the Myicolidae, as well.We place Taxon classificationAnimaliaCyclopoidaMyicolidaegen. nov.sp. nov.556C984A-88BE-54B3-AA4B-FAC730AE759Chttps://zoobank.org/5C31B845-08AB-455D-9249-29B7617CCA87Holotype ♂ (MABIK CR00250128) dissected and mounted on a slide, Site 11 , 07 Jul. 2020, leg. J. G. Kim.Male. Body  dissected and mounted on a slide, Site 22 , 31 May 2021, leg. J. Lee.Female. Body  and a single-segmented exopod of leg 4 (cf. two-segmented in P.bogilensis sp. nov.); P.australis has an aesthetasc on the second endopodal segment of the antenna (cf. this aesthetasc absent in P.bogilensis sp. nov.), the terminal antennal segment is 3.5 × longer than wide (cf. 1.28 × longer than wide in P.bogilensis sp. nov.), and the maxillary syncoxa lacks a claw-like process (cf. this process present in P.bogilensis sp. nov.); and P.ovilaxa has caudal rami which are 4.40 × longer than wide (cf. 2.96 × in P.bogilensis sp. nov.), the terminal antennal segment is 2.5 × longer than wide, and the maxillary syncoxa lacks the claw-like process.The genus ustralia  and the ustralia . These tTaxon classificationAnimaliaCyclopoidaPseudanthessiidaeE2AA7EA4-BF29-5546-A5ED-C4D03106245Bhttps://zoobank.org/99BB54CC-6289-4E0D-9B8C-8D4AE3EF5805Holotype ♀ (MABIK CR00250120) and intact paratypes 3 ♀♀ (MABIK CR00250121) preserved in 90% alcohol, and paratype ♀ dissected and mounted on a slide, Site 22 , 31 May 2021, leg. J. Lee; ♀ dissected and mounted on a slide, Site 23 , 24 Apr. 2021, leg. J. Lee and C. Y. Chang. Dissected specimens are retained in the collection of I.-H. Kim.Female. Body  and fer (bear), referring to the presence of the tongue-like dorsolateral processes on the genital double-somite.The specific name of the new species Pseudanthessiuslinguifer sp. nov. is its elongate caudal rami, which are 10 × longer than wide. Such long caudal rami are exhibited by four congeners: P.concinnus Thompson & Scott, 1903, P.dubius Sars, 1918, P.thorelli , and P.stenosus Kim & Hong, 2014. All of the other species in the genus have shorter caudal rami, at most 8.5 × longer than wide, as in P.deficiens Stock, Humes & Gooding, 1964  and two distal spines on the endopod of leg 4 (cf. one spine plus one seta in P.concinnus); from P.dubius in having the five-segmented urosome in the female  and four distal claws on the antenna (cf. a single large claw in P.dubius); and from P.thorelli in having one spine plus one seta on the exopod of female leg 5 (cf. two setae in P.thorelli). Pseudanthessiuslinguifer sp. nov. resembles P.stenosus which is known from Thailand  and paratype ♂ dissected and mounted on a slide, and intact paratypes 2 ♂♂ (MABIK CR00250122) preserved in 90% alcohol, Site 2 , 01 Jul. 2021, leg. J. G. Kim. Dissected paratype (♂) is retained in the collection of I.-H. Kim.Female. Body , alluding to the leaf-like inner seta of the maxillule.The specific name of the new species is from Latin Eupolymniphilus are slight. However, E.foliatus sp. nov. can be differentiated from its congeners by the key character, the leaf-like modified inner seta of the maxillule. This seta in other species of the genus is known to be simple and slender. Another characteristic feature of the new species is the presence of thick membranes on the distal part of the mandibular lash.Differences between species of Eupolymniphilus is somewhat variable among congeneric species. In the female, it is 3.5:1 in E.finmarchicus  according to the illustration of G. O. E.tenuicaudis , 1.50:1 in E.orientalis Kim, 2006, 1.03:1 in E.brevicaudatus Kim, 2009, 2.69:1 in E.occidentalis Kim, 2009, and 3.05:1 in E.mediterraneus Costanzo, Brugnano & Zagami, 2013. Thus, E.foliatus sp. nov., in which the caudal ramus is 3.33 × longer than wide, is comparable to the three species, E.finmarchicus, E.occidentalis, and E.mediterraneus. Furthermore, they differ from the new species, as follows: E.finmarchicus has five setae on the first segment of the antennule , seven aesthetascs on the male antennule (cf. six aesthetascs in E.foliatus sp. nov.), and a shorter terminal segment of the antenna which is 1.92 × longer than wide according to E.foliatus sp. nov.); and E.mediterraneus has a small body size, 0.75 mm in the female, and the terminal segment of the antenna bears four claws (E.foliatus sp. nov.).The length-to-width ratio of the caudal ramus in ntennule , and theur claws   and A.hasta .This is a fish-parasitic copepod, living in the gill cavity of the host. Known hosts of this copepod are the gobiid fishes Siphonostomatoida Burmeister, 1835Order Taxon classificationAnimaliaSiphonostomatoidaArtotrogidaeKim, 1996955E5926-FC7B-5B2B-BC51-7D591E0C5815One ♂, Site 4, 19 Jul. 2016; 1 ♀, 1 ♂, Site 11, 03 Jun. 2019; 2 ♂♂, Site 11, 10 Jun. 2020.Taxon classificationAnimaliaSiphonostomatoidaArtotrogidaeKim, 1996AAE7EFD1-D380-5570-A278-4D06FE9D1D15One ♀, 1 ♂, Site 11, 10 Jun. 2020; 2 ♀♀, 1 ♂, Site 21, 26 Apr. 2021.Taxon classificationAnimaliaSiphonostomatoidaArtotrogidaeKim, 199607421D6D-902D-52E8-8D83-141B42FC979BOne ♀, 1 ♂, Site 11, 10 Jun. 2020.Taxon classificationAnimaliaSiphonostomatoidaArtotrogidaeKim, 19969C4C8A1C-098F-563A-A2DC-856805DBB003One ♀, Site 11, 03 Jun. 2019; 5 ♀♀, Site 11, 10 Jun. 2019; 1 ♀, 10 ♂♂, Site 11, 10 Jun. 2020.Taxon classificationAnimaliaSiphonostomatoidaArtotrogidaeKim, 19961F43CA98-A5D8-5640-ACB6-0139D59C5E1BOne ♀, 5 ♂♂, Site 1, 28 Jun. 2021; 1 ♀, 4 ♂♂, Site 2, 01 Jul. 2021; 1 ♀, Site 3, 17 Jul. 2016; 10 ♀♀, 41 ♂♂, Site 7, 19 Jul. 2016; 2 ♀♀, 5 ♂♂, Site 12, 16 Mar. 2013; 1 ♀, 4 ♂♂, Site 14, 04 Jul. 2020.This species is the most frequently found artotrogid copepod in Korean waters; living on sponges, among sea weeds, and on submerged fishing nets in ports .Taxon classificationAnimaliaSiphonostomatoidaArtotrogidaeKim, 199629B2EF8D-064D-5E86-954D-7B1161E30B39Five ♀♀, Site 33, 11 Aug. 2020.Halocynthiaigaboja Oka, 1906.This copepod had been found only on the external surface of the tunicate Taxon classificationAnimaliaSiphonostomatoida AsterocheridaeEDC2C572-4DF3-5AF8-BA49-927F82CAB8A0https://zoobank.org/5654B945-0217-4D32-A0EB-2BF6D204BD4EHolotype ♀ (MABIK CR00250115) and paratypes 3 ♀♀, 2 ♂♂ (MABIK CR00250116) preserved in 90% alcohol, and paratypes 1 ♀, 1 ♂ dissected and mounted on a slide, Site 11 , 07 Jul. 2020, leg. J. G. Kim. Dissected paratypes  are retained in the collection of I.-H. Kim.Female. Body , indicating the discovery of the new species in the summer.The specific name Acontiophorus species. Aconiophorusestivalis sp. nov. has an 11-segmented antennule in the female; this feature is shared with three congeners, A.antennatus Hansen, 1923, A.scutatus  and A.zealandicus Sewell, 1944. Acontiphorusantennatus was redescribed by A.antennatus is ~ 4 × longer than wide in the female  and the third exopodal segment of leg 1 is armed with three spines and four setae . In A.zealandicus the male antennule is ten-segmented  and the oral siphon is extremely long, extending beyond the caudal rami . Therefore, A.antennatus and A.zelandicus can be distinguished from A.estivalis sp. nov. with confidence. Acontiophorusestivalis sp. nov. closely resembles A.scutatus. As noticeable differences between them, the caudal ramus of A.scutatus is 3 × longer than wide, and the oral siphon of the latter species extends to the caudal rami . Additionally, the first segment of the male antennule of A.scutatus bears an aesthetasc, according to the illustration of A.estivalis sp. nov.The segmentation of the antennule appears to be a reliable character for the differentiation of dal rami  0CEEC9D9-AAD8-5821-8A11-D116466BCF71Two ♂♂, Site 1, 28 Jun. 2021; 1 ♀, Site 3, 17 July. 2016; 1 ♀, Site 4, 03 Jun. 2019; 2 ♀♀, Site 5, 21 Jun. 2016; 1 ♀, Site 6, 21 Sep. 2020; 1 ♀, 2 ♂♂, Site 11, 20 Aug. 2020; 2 ♀♀, 1 ♂, Site 13, 03 Jul. 2020; 6 ♀♀, 6 ♂♂, Site 16, 04 Jul. 2020.Dermatomyzonnigripes is a cosmopolitan species, and has frequently been collected in Korean coasts. The host of this copepod is still unknown.Taxon classificationAnimaliaSiphonostomatoidaAsterocheridaeD5294558-6A7E-5C1C-8A97-17ABD371518Bhttps://zoobank.org/5F56B3F1-9731-49D8-A209-C6945F094AEAHolotype ♂ (MABIK CR00250117) preserved in 90% alcohol, Site 22 , 26 Apr. 2021, leg. J. Lee and C. Y. Chang; Paratype ♂ dissected and mounted on a slide, Site 15 , 04 Jul. 2020, leg. J. G. Kim. Dissected paratype is retained in the collection of I.-H. Kim.Male. Body  one of four setae on the outer lobe of the maxillule is positioned in middle in T.validus, whereas all of the four setae are distally positioned in T.pacificus sp. nov.; and (2) the third endopodal segment of leg 4 is armed with one spine plus four setae , but with one spine plus three setae  in T.pacificus sp. nov. These two differences are so significant that the Korean material should be separated from the type species as a new species. The proportional length of the caudal ramus and the developmental condition of the protopod of leg 5 also appear different between the two species, although these characters are subject to sexual dimorphism. Thermocheresvalidus was described on the basis of the female only.The discovery of this new species reinforces the taxonomic status of the genus dagascar . AlthougTaxon classificationAnimaliaSiphonostomatoidaCaligidaePillai, 19615F8C75B1-50B1-5CE2-8174-ADE035194577CaligusamblygenigtalisCaliguslongipedis: Ho and Lin, 2001: 188, fig. 9 . Pillai, 1961: 98, figs 8, 10; Ho and Lin, 2003: 56, figs 1, 2. MABIK CR00250989–CR00250995), Site 7, 21 Nov. 2019; 1 ♂, Site 11, 10 Jun. 2019.Two ♀♀, 5 ♂♂ .This species had been placed in the genus analysis . CaligusTaxon classificationAnimaliaSiphonostomatoidaCaligidaeGusev, 195172A9864E-0481-58AE-B626-1BCC94CA29D3One ♀, 2 ♂♂, Site 21, 26 May 2017; 1 ♂, Site 25, 06 Jul. 2016; 1 ♂, Site 26, 06 Jul. 2016; 3 ♀♀, 3 ♂♂, Site 27, 09 Jul. 2016; 2 ♀♀, 6 ♂♂, Site 28, 07 Jul. 2016; 4 ♀♀, 1 ♂, Site 29, 09 Jul. 2016; 1 ♀, Site 30, 17 Oct. 2020.Caligusorientalis is a parasite of coastal marine and brackish-water fish in the East Asian waters. It has a wide host range and has been reported from over 20 fish species of different orders and families  which has been treated as a junior synonym of Parajulispoecilepterus .The genital complex of the female of this caligid is characteristically triangular. The only known host of this copepod was Taxon classificationAnimaliaSiphonostomatoidaCaligidaeShen & Li, 1959DC048E6C-F220-5F37-B482-06C0392D6C8BFour ♀♀, 1 ♂, Site 11, 16 Apr. 2014; 1 ♀, 1 ♂, Site 20, 05 Jun. 2020; 1 ♀, Site 26, 06 Jul. 2016; 1 ♀, 2 ♂♂, Site 31, 15 Nov. 2020.Konosiruspunctatus , at a market at Gonam, Hadong, south coast , 25 Jul. 2012, leg. I.-H. Kim.1 ♀ and 1 chalimus from the skin of the fish Body Fig.  narrow. Sternal furca Fig.  narrow; Male. Body  as a host of C.undulatus, which was the first host record. In the present study, we report Konosiruspunctatus as an additional host record. The fish hosts S.zunasi and K.punctatus live on East Asian coasts, sometimes entering bays or brackish waters. It is conceivable that C.undulatus and other caligids may detach from the hosts due to the salinity change when the hosts approach brackish waters.A female specimen from Site 11 exhibited a shrunken genital complex with undulated lateral margins as observed in the type material of