Lycenchelys delanglei Thiel, Knebelsberger, Chernova & Eidus, 2025, sp. nov.

Lycenchelys delanglei sp. nov. Common name: de Langle´s eelpout (Figures 1–3 & 6; Table 1) Holotype. ZMH 26277, female, 196 mm SL, voucher specimen code MT 10106, RV ‘Akademik M.A. Lavrentyev’, AGT haul 9-9, Bussol Strait, southern of Simushir Island, Agassiz trawl, 46˚15.7΄N; 152˚03.1΄E, 3580 m depth, 27 July 2015. Paratypes. Three specimens; ZMH 26278, female, 157 mm SL, voucher specimen code MT 10107, same collection data as holotype. ZMH 26279, female, 157 mm SL, voucher specimen code MT 10112, RV ‘Akademik M.A. Lavrentyev’, AGT haul 9-10, Bussol Strait, southern of Simushir Island, Agassiz trawl, 46˚15.7΄N; 152˚03.1΄E, 3517 m depth, 27 July 2015. ZMH 26280, male, 199 mm SL, voucher specimen code MT 10114, same collection data as ZMH 26279. Diagnosis. A species of Lycenchelys from the Western North Pacific with 120–121 vertebrae; it differs from congeners of the area by the following combination of characters: comparatively long abdominal body part (precaudal vertebrae 28–29) and short caudal body part (caudal vertebrae 91–93); suborbital pores numerous (10– 12); postorbital pores 4; interorbital and occipital pores absent; preoperculomandibular pores 4 + 5; dorsal-fin rays 114–117; 2–3 free pterygiophores at the beginning of dorsal fin; anal-fin rays 96–98; pelvic-fin rays two; pectoral-fin rays 16–17; lateral line absent. Description. Counts and measurements are provided in Table 1. Body relatively long (Fig. 2), its cross section elliptical at both abdominal and caudal regions and somewhat more round at nape and compressed laterally near tail. Head elongate, ovoid, flat top, dorsal profile evenly declined from nape to relatively steeply sloping snout tip (Fig. 3). Eye ovoid, just entering dorsal profile of head. Interorbital space convex. Gill slit extending ventrally to the level of lower pectoral base. Opercular flap well developed. Mouth inferior, posterior edge of upper jaw reaching vertical through anterior margin of eye. Nostril tube not or just barely reaching upper lip when depressed forward. Snout rounded. Labial lobe of lower jaw developed. Teeth conical, relatively large on jaws; upper jaw with single continuous row, anteriormost teeth larger than posterior teeth, short additional row with 3–4 small teeth behind anteriormost teeth; lower jaw with 2–3 irregular rows anteriorly and single row posteriorly; 4–8 small and conical vomerine teeth irregularely arranged; palatine teeth in single row. Head pores well developed and distinct (Fig. 3). Two nasal pores, anterior one set just in front of nostril tube, other situated dorsoposteriorly. Suborbital pores 10–12, 8–9 pores arising from ventral ramus of bone chain under eye and 2–3 from ascending ramus behind eye. Postorbital pores 4, distance between 1 st and 2 nd pores longest of those between adjacent pores (Fig. 3). Mandibular pores on lower jaw 5, 4 arising from dentary and one from anguloarticular. Preopercular pores 4. Interorbital and occipital pores absent. Body lateral line completely absent. *No. epurals + on upper hypural plate + on lower hypural plate; **on upper limb + on lower limb. Dorsal fin origin above anterior third of pectoral fin; 2–3 free pterygiophores at the beginning of dorsal fin; lower tip of first pterygiophore of dorsal-fin is between tips of neural spines of sixth and seventh or seventh and eighth vertebrae. Pterygiophore of last dorsal ray is associated with third or fourth preural vertebra. Anal fin origin associated with first caudal vertebra. 3–4 pterygiophores of anal fin inserted anteriorly to haemal spine of first caudal vertebrae; pterygiophore of last anal ray associated with second preural vertebra. Pectoral fin origin at body midline. Ray tips of the pectoral fin exserted, the middle and lower ones significantly more than the upper ones. Pelvic fin small, its length shorter than snout. Caudal fin with 2 epural, 4–5 upper and 3–4 lower hypural rays. Scales absent on head, nape, thorax and pelvic fin. Scales present on lower part of pectoral fin and its basis. Scales small and cycloid, present on body, tail, dorsal and anal fins, extending to about three fourth of fin height in two largest individuals (ZMH 26277 and ZMH 26280). Scales on dorsum before dorsal fin origin; extending anteriorly somewhat in front of line connecting upper ends of gill openings (Fig. 3). Belly scaled; extending anteriorly not quite to base of pectoral fin (Fig. 3), in largest specimen (ZMH 26280) also a few scales ventrally between bases of pectoral and pelvic fins. Gill rakers short, those on upper limb narrower and more pointed than those on lower limb. Pseudobranch filaments relatively long. Pyloric caeca not developed. Fresh color (Fig. 2). Head, pectoral fin, dorsal and anal fins dark brown to blackish. Lips, head pores and base of pectoral fin lighter. Body more brownish anteriorly to anus, a lighter ring around anus. Leight grey to leight beige colored posteriorly from anus. Eyes black. Preserved color (Fig. 2 & 3). Specimens faded in comparison to fresh color. Head, pectoral fin and partly margin of vertical fins brownish. Body light beige. Eyes black. Peritoneum and lining of orobranchial cavity dark brown. Etymology. The species is named after Paul Antoine Fleuriot de Langle (1744–1787), a French naval commander and explorer. Together with Jean-François de La Pérouse, de Langle led the La Pérouse expedition as a ship´s captain. In 1787 the expedition ships navigated in the waters of the Kuril-Kamchatka Trench, where the new species was discovered. The La Pérouse expedition passed also through the Bussol Strait, shortly before Langle’s death in Samoa during an encounter with natives. The Bussol Strait was named after the frigate “La Boussole”, one of the ships of the La Pérouse expedition. The Bussol Strait is located near the site where the new species was found. Distribution. Lycenchelys delanglei sp. nov. is known only from two very closely spaced AGT hauls performed at station 9 of SokhoBio expedition at the western slope of the upper margin of the Kuril-Kamchatka Trench. Environmental conditions. Bottom sediments in the box-corer (BC) at the place of capture contained mainly silt (74%) followed by clay (24%) and sand (2%; Kamenev et al. 2022). The abundance of fauna caught with BC at station 9 of SokhoBio expedition was characterized by a high proportion of polychaetes (81%), followed by bivalves (6%; Kamenev et al. 2022). A species of genus Yoldiella (Family Yoldiidae Dall, 1908), was the dominant species among bivalve molluscs at station 9 (Kamenev 2018). Feeding ecology. It is highly probable that the mussel shells seen on the radiographs (Fig. 6) belong to Yoldiella sp. Three out of the four type specimens of L. delanglei sp. nov. contained high numbers of shells of Yoldiella sp. in their stomachs, so this may be one of the main food items of L. delanglei sp. nov. at this site. DNA barcode. For the holotype ZMH 26277 and the three paratypes ZMH 26278–80 of Lycenchelys delanglei sp. nov., full COI barcodes (652 bp) were obtained and uploaded to GenBank (https://www.ncbi.nlm.nih.gov/genbank/) with the following accessions: ZMH 26277: PQ585656, ZMH 26278: PQ585657, ZMH 26279: PQ585658, ZMH 26280: PQ585659. Tissue samples and DNA isolates were stored in the DNA and tissue collection of the DZMB. The comparisons of the haplotype sequence of L. delanglei sp. nov. with all published DNA sequences on NCBI using MegaBLSAT algorithm showed that the closest matches were with four sequences of Lycenchelys lenzeni Thiel, Knebelsberger & Eidus, 2018 (GeneBank accessions:MG650294.1, MG650295.1, MG650296.1, MG650297.1) with a sequence similarity of 98.47%, followed by two specimens of Lycenchelys jordani (Evermann & Goldsborough, 1907) with sequence similarities of 97.24 (GeneBank accession: FJ164740.1) and 97.39% (GeneBank accession: FJ164744.1) and 8 specimens of Lycenchelys aratrirostris Andriashev & Permitin, 1968 (sequence similarities 96.90–97.21%; GeneBank accessions: HQ713029.1, HQ713030.1, HQ713032.1, HQ713033.1, HQ713034.1, HQ713035.1, HQ713036.1, HQ713037.1). Comparative notes. We compared Lycenchelys delanglei sp. nov. with 25 other Lycenchelys species known from the Western North Pacific based on their characters according to Anderson (1995), Anderson & Balanov (2000), Anderson & Imamura (2002), Fedorov (1995a,b), Fedorov & Andriashev (1993), Kawarda et al. (2020), Shinohara & Anderson (2007), Shinohara & Matsuura (1998) and Toyoshima (1985). Comparisons of main characters are provided in Table 3, where differences between the new species and known species are indicated in bold. The most significant differences between the new species and congeners are provided below. Twenty-one Lycenchelys species from the Western North Pacific possess fewer suborbital pores than the new species (10–12 suborbital pores). Only the following four species have ten or more suborbital pores (number of compared characters for each of the following species in brackets): L. albomaculata Toyshima, 1983 (9–11), L. hippopotamus Schmidt, 1950 (9–10), L. melanostomias Toyshima, 1983 (8–10), L. ratmanovi Andriashev, 1995 (8–10). The new species differs from the latter four species by the absence of interorbital pores versus one interorbital pore in L. albumaculata, L. melanostomias and L. ratmanovi and one or two pores in L. hippopotamus. Moreover, L. delanglei sp. nov. has a higher number of precaudal vertebrae (28–29) than L. albomaculata (22–25), L. hippopotamus (23–24), L. melanostomias (22–25) and L. ratmanovi (21–23). Furthermore, the new species has a lower number of anal-fin rays (96–98) than L. albomaculata (101–109) and L. hippopotamus (111–120) as well as a lower number of dorsal-fin rays (114–117) than L. hippopotamus (124–133) and a higher number of dorsal-fin rays than L. ratmanovi (105–110). Lycenchelys delanglei sp. nov. differs from L. melanostomias in having 2–3 free pterygiophores at the beginning of dorsal fin, no occipital p