New species of Furculanurida (Collembola, Neanuridae, Pseudachorutinae) from the Luquillo Mountains, Puerto Rico

Abstract A new species of Furculanurida is described and illustrated. Furculanuridabistribussp. nov. differs from other species of the genus by the presence of three eyes, three setae on the dens, and the white and purple coloration pattern. A key for identification of the world species of the genus is included.


Introduction
In Puerto Rico, most studies of arthropod community dynamics have been done in the Luquillo Mountains. Designated as a US Experimental Forest in 1956, it became part of the International Network of Biosphere Reserves in 1976 (González and Barberena 2018;Quiñones et al. 2018;Richardson 1999). Four easily distinguishable forest types are dominated by an assortment of distinctive tree species. The Tabonuco forest long. However, the more recently described Furculanurida species include specimens without the full development of the furcula (Zon et al. 2014). Zon et al. concluded that Furculanurida can only be separated from Pseudachorutes Tullberg, 1871 by a conditional combination of characters, i.e., "eyes less than 8+8, or, when 8+8, microchaeta ms absent on Ant. IV". Similarly, differences with Stachorutes Dallai, 1973 would be "mucrodens complete, or, if mucro absent, ms absent on Ant. IV" (Zon et al. 2014: 496). Therefore, these genera need an extensive revision to clarify the morphological differences between them.

Materials and methods
Abbreviations a.s.l above sea level

Ventral Tube
The material used to describe the species was collected during the Collembola microhabitats project at the Luquillo Mountains, as part of a survey conducted in three forest types. Collembola were extracted using Berlese-Tullgren funnels into 95% ethanol. They were cleared using Nesbitt solution and fixed on slides using Mac André II solution (Mari Mutt 1979). The slides were then dried in a slide warmer at 45-50 °C for seven days. Finally, each specimen was labeled with its collecting data. Specimens were examined with a Leica DM500 phase-contrast microscope. The drawings were made with the aid of a drawing tube. All the type material is deposited at International Institute for Tropical Forestry laboratory. Diagnosis. Eyes 3+3 eyes. Post antennal organ in rosette with 5 or 6 vesicles. Ant IV with six sensilla. Seta a0 on head absent. Mandible with four teeth. Dens with three setae. Unguis without internal tooth.
Description. Average body length: adults 1009 µm (n = 5); juveniles 847 µm (n = 2). Specimens in ethanol with antenna and abdomen evenly grey, ocular patch dark; head, legs III, and furcula light grey; thorax, legs I and II white to light purple (Fig. 1). Granulation coarse. Body setae comprising short, smooth and thin setae, and long and smooth sensorial setae.
Dorsal chaetotaxy: ordinary setae smooth, distributed as in Figure 2. Th I with 2+2 setae; Th II and III with one dorsolateral seta posteriorly displaced. Sensory setae (s) clearly differentiated, in position p3 and p6 in Th II and III and in position p3 in Abd I-V; S-chaetotaxy formula = 022/11111.
Etymology. Bistribus, Latin for two times three, in reference to the presence of 3+3 eyes and 3+3 setae on dens, diagnostic characters of the species.
Ecology. Furculanurida bistribus sp. nov. was extracted from leaf litter and mosses in both dry and rainy seasons during November 2014, and May and August 2015. Table 1. Furculanurida species with disputed generic placement and their taxonomic history.

Furculanurida Thibaud and Palacios-Vargas 2000
Presence of four teeth in the mandible furculata (Salmon, 1956) Kenyura Furculanurida Massoud (1967) Furcula developed and post-antennal organ present perplexa (Salmon, 1956) Hypanurida Furculanurida Massoud (1967) Reduced furcula Hypanurida Thibaud and Palacios-Vargas (2000) Reduced furcula and 3-4 setae in dens + Generic placement according to cited authors (current genus in bold). ++ Character to justify the placement in their current genus. Mandible with 10 teeth .. Discussion Furculanurida bistribus sp. nov. is placed in Furculanurida because many of its characters are similar with those of the other species of that genus, and it matches the current genus diagnosis: apical bulb trilobed, long setae present on Ant IV, maxilla styliform, furcula fully developed, and ordinary setae on the body short but sensory setae long (Queiroz and Fernandes 2011). Although the presence of one tooth on the unguis is observed in most Furculanurida, there are two exceptions where the unguis is toothless: F. africana and the new species described here. In any case, the inner tooth on the claw is usually considered as a specific, not a generic character (Zon et al. 2014). The antennal chaetotaxy is also useful to characterize the genus; the new species has antennal characters of Furculanurida: apical vesicle trilobed, microsensillum absent, and presence of six S-sensilla and long setae on Ant IV (Queiroz and Fernandes 2011). The low number of dental setae is a character shared with Hypanurida perplexa Salmon, 1956, but the position of this species is controversial because of the reduction of the furcula (Queiroz and Fernandes 2011). Although morphological characters, including furcal reduction, appear similar between some Furculanurida (including F. bistribus sp. nov.) and Stachorutes (Zon et al. 2014), the geographic separation of the two genera is remarkable. The genus Furculanurida was established for three sub-Saharan African neanurids: Micranurida africana, Kenyura furculata Salmon,1956, and Hypanurida perplexa (see Massoud 1967). Subsequently, other species were described or included in Furculanurida from the Lesser Antilles, Guatemala, Brazil, French Guiana, Tanzania, Morocco, Nepal, and Ivory Coast (Queiroz and Fernandes 2011;Zon et al. 2014). The genus, thus, conforms to a general Gondwanan distribution, with a few exceptions, like Furculanurida langdoni which is found in North America. In contrast, Stachorutes exhibits mostly an Holarctic distribution, with species known from China, France, Poland, Russia, Slovakia, Spain, and North America, except for a single species from Africa (Tanzania) (Simon-Benito et al. 2005;Fanciulli et al. 2017).
According to Queiroz and Zeppelini (2017), there are key diagnostic characters that define two groups of Pseudachorutinae in the Neotropics, which are chaetotaxy of antennae, head, thorax, and tibiotarsi. Furculanurida bistribus sp. nov. exhibits many similarities with Arlesia group of genera. In the antennal chaetotaxy, the only difference was the absence of S10 sensu Queiroz and Zeppelini (2017). Regarding head and thorax chaetotaxy, the main characters are similar, i.e. the absence of setae c2 and c3 and the presence of p1, p2 and p3 on head, the presence of only 2+2 setae on Th I, and one posterior setae displaced laterally on Th II and III. In consequence, this description reinforces the need for a revision of Furculanurida, as not only F. bistribus sp. nov. but possibly other species of Furculanurida might present characters that fit the pattern displayed by the Arlesia-group of genera sensu Queiroz and Zeppelini (2017).
Despite the differences of the new species with the most recent genus diagnosis of Furculanurida (Queiroz and Fernandes 2011), we place F. bistribus sp. nov. in this genus because of the fully developed furcula in this species (Fig. 11) and its distribution, despite the number of setae on the dens. Inclusion of the new species in this genus thereby enlarges the generic diagnosis to include species with 3-6 setae on the dens. The characters that place the new species close to Stachorutes are of uncertain generic value and need more studies (Bernard 2007;Zon et al. 2014, Neves et al. 2019. Furculanurida bistribus sp. nov. has this unique combination of characters: six sensilla on Ant IV, 3+3 eyes, three setae in the dens, and the absence of an internal tooth on the unguis, combined with its color pattern. Members of Furculanurida have between zero and eight eyes per side; F. bistribus sp. nov. has 3+3 eyes, though some specimens of F. arawakensis may have this number (usually 4+4 eyes). All the described species have a fully developed furcula, but more dental chaetae than the new species. Leaving aside the unique characters of F. bistribus sp. nov., it is more similar to F. arawakensis from which it differs by the presence of four teeth on mandibles (versus seven), less dental chaetae (3 versus 6), and the absence of tooth on unguis. The differences between all the species of the genus are summarized in Table 2.