Lycenchelys delanglei, Thiel & Knebelsberger & Chernova & Eidus, 2025

Lycenchelys delanglei sp. nov.

Common name: de Langle´s eelpout

( Figures 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 & 6 View FIGURE 6 ; Table 1 View TABLE 1 )

Holotype. ZMH 26277 View Materials , 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 View Materials , female, 157 mm SL, voucher specimen code MT 10107 , same collection data as holotype . ZMH 26279 View Materials , 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 View Materials , 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 View TABLE 1 . Body relatively long ( Fig. 2 View FIGURE 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 View FIGURE 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 View FIGURE 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 View FIGURE 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.

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 View FIGURE 3 ). Belly scaled; extending anteriorly not quite to base of pectoral fin ( Fig. 3 View FIGURE 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 View FIGURE 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 View FIGURE 2 & 3 View FIGURE 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 View FIGURE 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 View Materials and the three paratypes ZMH 26278–80 View Materials 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 View Materials : PQ585656, ZMH 26278 View Materials : PQ585657, ZMH 26279 View Materials : PQ585658, ZMH 26280 View Materials : 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 View 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 pores and two pelvic-fin rays, whereas L. melanostomias has no such free pterygiophores, two occipital pores and three pelvic-fin rays. In addition to L. melanostomias , the new species is morphologically most similar to Lycenchelys plicifera Andriashev, 1955 . However, L. delanglei sp. nov. has a lower number of vertebrae (120–121 vs. 122–126) and a higher number of suborbital pores (10–12 vs. 8–9) as well as of postorbital pores (4 vs. 1–2) than L. plicifera . Furthermore, the new species has a lower number of free pterygiophores (2–3) at the beginning of dorsal fin than L. plicifera (6–7, Table 3 View TABLE 3 ).

The species L. birsteini Andriashev, 1958 has not been compared with the new species as we found support for the opinion of Anderson (1995) that it should be regarded as a synonym of L. plicifera . The number of 6–7 free pterygiophores at the beginning of dorsal fin is a result of our own analyses of radiographs of the holotypes and paratypes of L. plicifera and L. birsteini . In comparison with Parin (2014), who stated that in the case of L. birsteini , its holotype has 7 and its paratype has 8 free pterygiophores at the beginning of dorsal fin, we estimated also 7 free pterygiophores in the holotype but only 6 free pterygiophores in the paratype of L. birsteini . Furthermore, we counted 6 free pterygiophores in both the holotype and paratype of L. plicifera supporting the assumption that L. plicifera and L. birsteini are the same species. In addition, Anderson (1995) pointed out that the white abdominal skin fold (plica) after which Andriashev (1955) named L. plicifera is also present in the paratype of L. birsteini (ZIN 34669a). Due to these and other very similar morphological characteristics we follow the opinion of Anderson (1995) that L. birsteini should be regarded as a junior synonym of L. plicifera .

Comparisons of DNA barcodes revealed that L. delanglei sp. nov. can be distinguished from other species; however, relatively high sequence similarity (less than 2% different) was found with L. lenzeni from the Western North Pacific ( Table 3 View TABLE 3 ). The genetic distance to L. jordani from the Eastern North Pacific is more than 2%. However, these two species differ morphologically from the new species. Lycenchelys delanglei sp. nov. has lower numbers of vertebrae (120–121 vs. 126–130), dorsal-fin rays (114–117 vs. 118–122), anal-fin rays (96–98 vs. 105–108) and a higher number of suborbital pores (10–12 vs. 6–7) and free pterygiophores at the beginning of dorsal fin (2–3 vs. 0; Table 3 View TABLE 3 ) than L. lenzeni . The new species has a lower number of total vertebrae (120–121) than L. jordani (128–135) and differs from the L. jordani , for instance, also in having a higher number of precaudal vertebrae (28–29 vs. 24–26), a lower number auf caudal vertebrae (91–93 vs. 102–110), less dorsal-fin rays (114–117 vs. 119–124), less anal-fin rays (96–98 vs. 106–114), less pelvic-fin rays (2 vs. 3), a higher number of suborbital pores (10–12 vs. 7–8) and a higher number of postorbital pores (4 vs. 3). Furthermore, L. aratrirostris , occurring in the Southern Ocean, showed a moderate sequence similarity with L. delanglei sp. nov. But the new species differs from L. aratrirostris in having higher numbers of dorsal-fin rays (114–117 vs. 97–107), anal-fin rays (96–98 vs. 79–89), total vertebrae (120–121 vs. 101–110) and a lower number of pelvic-fin rays (2 vs. 3).