A revision of Syllidia (Psamathini, Hesionidae, Polychaeta)

Syllidia Quatrefages, 1866 (Psamathini, Hesionidae, Polychaeta) is revised based on examination of all extant types, other museum specimens, and a large number of newly collected specimens. Syllidia hongkongensis, new species, is described from Hong Kong and Hawaii, and Syllidia armata Quatrefages, 1866 from western France is redescribed. Syllidia hongkongensis is unique within the genus in having neuropodial lobes and neurochaetae from segment 3, rather than from segment 4. The generic names Magalia Marion and Bobretzky in Marion 1874 and Pseudosyllidia Czerniavsky, 1882 are treated as junior synonyms of Syllidia, and the specific names Magalia assimilis Pryde, 1914, M. capensis McIntosh, 1924, and Psamathe britannica Chamberlin, 1919 as junior synonyms of S. armata; the latter two represent new synonymies. A lectotype is designated for P. britannica. Syllidia inermis (Ehlers, 1912) from the Antarctic is treated as incertae sedis; it belongs within Psamathini but is not a member of Syllidia. Syllidia liniata Hartmann‐Schröder, 1962 from Peru appears close to S. armata, but is regarded as a nomen dubium and requires recollection of specimens and redescription.


Apomorphies
Presence of well-developed, paired jaws with a median stylet.

Remarks
Marion and Bobretzky (in Marion 1874) erected Magalia for the new species M. perarmata from Marseille in southern France. As generally agreed in more recent literature, the two type species are considered synonymous (see Remarks for S. armata), and Magalia consequently also becomes a junior synonym of Syllidia.

Apomorphies
None currently known (see Remarks for S. hongkongensis).

Colour
Live specimens opaque to transparent, unpigmented except for dark brown ventral longitudinal midline, usually on posterior part of body (Figure 2). Gut yellowish, gut wall of last six or seven segments with white pigment speckles. Eyes red. Jaws dark brown, median stylet yellowish. Preserved specimens white to yellowish, eyes dark red, ventral longitudinal pigmentation usually retained.

Reproduction and development
Syllidia armata has an extended reproductive period, Cazaux (1970) recorded mature specimens from early summer to November in Arcachon near Bordeaux in France, and Rasmussen (1956) from May to October in Denmark. The eggs are 50-60 mm and colourless and the larvae are planktotrophic; the different stages were described in detail by Casanova (1954) and Cazaux (1970). They settle at a stage when they have about eight segments, and jaws start to develop at 10-14 segments. In contrast to the closely related Nereimyra punctata (O. F. Mü ller, 1776) (see Schram and Haaland 1984;Pleijel 1998), there are no traces of a median antenna in any early stages. The development described by Cazaux is in full agreement with observations from early stages from Sweden, with the exception that Cazaux reported the presence of a few capillary notochaetae in the late planktonic and newly settled stages; this requires further examination.

Habitat
Syllidia armata occurs in sand, gravel, and rocky substrata, 0-230 m depth; it is also recorded from mud bottoms in the literature Hartmann-Schrö der 1962).

Distribution
As seen from examined specimens, S. armata occurs in South Africa, Italy, Spain, Mediterranean and Atlantic coasts of France, and up to Sweden and Denmark in the north. Additional records from the literature include Amoureux (1976) and Amoureux and Gantès (1976) from Morocco, Langerhans (1880) from Madeira, Augener (1918) from Senegal, Hartmann-Schrö der (1982) from Guinea-Bissau, Day (1967) from South Africa, Ben Eliahu (1972) from Suez, and Rullier (1974) from Florida. See also Figure 9.

Remarks
Quatrefages, in his original description of S. armata, reported the presence of capillary notochaetae. As his description in all other respects agrees well with the description above, and as no notochaetae have been observed in any European specimens, we believe this was an error.
Marion and Bobretzky (in Marion 1874) introduced the new species Magalia perarmata from Marseille in southern France. They did not compare it to or mention Quatrefages' description of S. armata, possibly due to Quatrefages statement of the presence of capillary notochaetae. There is no extant type or other original material accompanying either of the two species names, but at present we see no need to designate neotypes. We agree with previous studies that the two are synonymous (e.g. Day 1967;Kirkegaard 1992;Pleijel 1998) as only one species is known from European waters. For the same reason we consider Pryde's (1914) species M. assimilis from the North Sea, also without extant types, as a junior synonym of S. armata. Pryde (1914), in his original description of Magalia assimilis, noted the presence of prolonged teeth on the blades, but then incorrectly assumed them to be absent from M. perarmata since they had not been described by Marion and Bobretzky (1875). All examined specimens, from the Mediterranean and elsewhere, have some chaetal blades with prolonged teeth. Pryde, similarly to Marion and Bobretzky, did not make any reference to Quatrefages' species. Chamberlin (1919) introduced Psamathe britannica. Although he had examined no specimens and did not provide any description of the species, he named it for the specimen from Ireland that McIntosh (1908) had referred to Castalia arctica Malmgren, 1867 (junior synonym of Nereimyra aphroditoides Fabricius, 1780 cf. F. Pleijel and A. Nygren, in preparation). According to McIntosh's (1908) original description, there was only one specimen, but re-examination of his material shows at least two specimens to be present (two anterior ends, one median part, and one posterior end). Although not previously recognized as such, these specimens (or minimally one of them) are actually the types for Chamberlin's species P. britannica. Of these specimens at least one anterior end clearly belongs to Syllidia, as seen from the everted proboscis with paired jaws and a median, ventral stylet. This is also the same specimen that was used for McIntosh's illustration Figure 14 on Plate LVIII, and we here designate it as lectotype. We therefore agree with Chamberlin that McIntosh's specimen was misidentified, but disagree with him on both the generic assigment and on the erection of a new species; instead we regard P. britannica as a junior synonym of S. armata. This is a new synonymy.
Syllidia capensis was described by  as Magalia capensis) from South Africa based on a single, incomplete specimen. McIntosh did not mention any depository and his type is not present at BMNH, at the National Museum of Scotland, or at the South African Museum, and it is therefore here considered lost. The new species was justified by the presence of chaetae with tips possessing long, delicate, and hair-like terminal pieces. However, examination of other South African specimens revealed no chaetal, parapodial, or other consistent morphological differences from S. armata, and we therefore here treat the name S. capensis as a junior synonym of S. armata. This is a new synonymy as well.
Several authors (Day 1967;Kirkegaard 1992;Hartmann-Schrö der 1996) have reported more than 10 papillae on the terminal proboscis ring. Nevertheless, all examined specimens where the proboscis was examined (ca 50) were provided with 10 papillae, as is the case also in closely related taxa, including Nereimyra Blainville, 1828 and Sirsoe Pleijel, 1998.

Apomorphies
Possibly the presence of neurochaetae on segment 3 (see Remarks).

Colour
Live specimens opaque to transparent, unpigmented except for brown ventral longitudinal midline, usually on posterior part of body. Eyes red. Jaws dark brown, median stylet opaque. Preserved specimens yellowish with weak transverse darker pigmented bands.

Reproduction
Several sexually mature specimens observed, both from Hong Kong and Hawaii. Mature female from Hong Kong with egg diameter about 45 mm.

Habitat
At the type locality with shell sand, gravel, and stones with calcareous red algae (Corallina sp.), low tide; down to 5 m depth in Hawaii.

Distribution
Presently known only from Hong Kong and Honolulu, Hawaii.

Remarks
Syllidia hongkongensis is clearly a member of Syllidia, as seen from the presence of paired, ventro-lateral jaws and a median stylet. Syllidia hongkongensis differs from all other Syllidia in the absence of neurochaetae on segments 1 and 2, rather than on segments 1-3. Hesionids go through a number of ontogenetic stages that involves reduction of chaetae and parapodial lobes on the anteriormost segments, such that most taxa have an adult condition with chaetae appearing first from segment 4 or 5 (see Pleijel 1998 and references within). It is therefore important to compare fully grown stages, and the adult status of our specimens of S. hongkongensis is evidenced by the presence of eggs and sperm in several of the animals. However, the unique presence of chaetae on segment 3 does not necessarily constitute an apomorphy for S. hongkongensis; for example, it is instead a plesiomorphy if S. hongkongensis is the sister to remaining Syllidia. The most closely related taxa to Syllidia, according to Pleijel (1998), are the sister group Nereimyra and Bonuania, and then Sirsoe, and these taxa have members where the chaetae start on segment 4 (Nereimyra), but also on segment 2 or 3 (Bonuania and Sirsoe). Furthermore, if the presence of chaetae from segment 3 indeed is an apomorphy for S. hongkongensis, then we may instead lack diagnostic features for S. armata (and possibly also for the lesser well-known members of Syllidia). Further characters are required to resolve these issues.
The specimens from Honolulu are in less good condition than those from Hong Kong. Nevertheless, they clearly are members of Syllidia as seen from, for example, the presence of similar jaws. Furthermore, all specimens from Honolulu, including mature ones, have chaetae present from segment 3, and based on this we refer them to S. hongkongensis.

Etymology
Named for the type locality, Hong Kong.

Remarks
Ehler's types have not previously been recognized as such, but comparison of his description with specimens and labels leaves no doubt that they constitute his original ones. They were collected during the British National Antarctic Expedition 1901-1904 (when the R/V Discovery was blocked for several years in the ice in McMurdo Sound at Ross Island), probably by the marine biologist Thomas Vere Hodgson, specialist of hydroids and jellyfishes. They include one entire specimen, one specimen with the posteriormost part missing, and four median pieces, all in excellent condition. However, examination of these specimens indicates that they do belong within Psamathini but are not members of Syllidia; among other features, they lack the jaws of Syllidia, and the neuropodia and neurochaetae start on segment 5, not on segment 3 or 4. Instead they likely belong to Psamathe Johnston, 1836; the issue will be further detailed in a forthcoming revision of Psamathe (F. Pleijel, in preparation).
As for the other records of S. inermis. Averincev (1972) reported it from Ross Sea and Davis Sea in the Antarctic, but we have not had the possibility to examine his specimens. The descriptions in Hartman (1964) and Knox and Cameron (1998) are based on Ehler's original description and include no new specimens or observations, whereas Hartmann-Schrö der and Rosenfeldt (1988) reported one specimen of this species (as S. cf inermis) from the Antarctic Peninsula. This specimen is unfortunately in very poor condition, and the only statements we can make is that it is likely a member of Psamathini but not of Syllidia.

Apomorphies
None currently known.

Description
Holotype in poor condition, consisting of anterior part of 18 segments and posterior part of eight or nine segments (posteriormost segments and pygidium missing), 3 and 1.5 mm long, respectively. Prostomium rounded rectangular, slightly longer than wide (but see Remarks). Nuchal organs lateral, mid-dorsally well separated. Proboscis everted, anterior part dissected and damaged, jaws and terminal ring of papillae no longer present. Neuropodial lobes and neurochaetae absent segments 1-3. All cirri missing. Median neurochaetae with longer blades than dorsal and ventral ones; ventralmost ones shortest. Chaetal shafts internally camerated. Several median chaetal blades with prolonged teeth.

Colour
Uniformly yellowish brown; no traces of pigmentation present.

Distribution
Only known from the type locality.

Remarks
Hartmann-Schrö der, 1962 described S. liniata from a single specimen from Peru, and no other specimens have been reported to date. Syllidia liniata is similar to S. armata in having neurochaetae from segment 4, and at present there are no actual characters to support keeping the two separate. Hartmann-Schrö der (1962) distinguished S. liniata from S. armata based on the shape of the jaws, the shape of the prostomium and the first two segments, and the dorsal pigmentation with transverse stripes on the anteriormost segments. However, her illustration of the jaws agrees with S. armata, and the difference in shape of prostomium could not be substantiated from examination of the specimen; it is slightly wider than long but this is the case also in specimens of S. armata with everted proboscis. The reported pigmentation is not shown on the original illustration and is no longer present on the specimen. In view of the poor condition of the single known specimen, we here treat it as a nomen dubium within Syllidia. A redescription based on newly collected specimens is required.