Osteodiscus lindbergi, Chernova & Thiel, 2025

Chernova, N. V. & Thiel, R., 2025, A new species of the genus Osteodiscus (Cottoidei: Liparidae) from the Kuril Basin (Sea of Okhotsk, western North Pacific), Proceedings of the Zoological Institute of the Russian Academy of Sciences 329 (1), pp. 3-12 : 5-7

Osteodiscus lindbergi sp. nov.

( Figs 1–2 , 3A, B )

Holotype. ZMH 28701 , female 92.6 mm SL, – TL; Kuril Basin (southern part of the Sea of Okhotsk), 46°57.0' N 151°00.4' E, 3306 m depth, 21.07.2015, RV “ Akademik M.A. Lavrentyev ”, cruise 71, station 7–11, Agassiz trawl; collector I. Eidus. Condition: end of caudal fin missing; skin on posterior part of body lost.

Paratypes (2). ZMH 28702 , female ca. 79 mm SL, – TL; same collection data as holotype. Condition: skin on head and body lost; end of tail (obviously 2 or 3 vertebrae) and caudal fin missing . ZMH 28671 , juvenile 50.9 mm SL, 57.3 mm TL; Kuril Basin, 48°03.0'N, 150°00.3'E, 3348 m depth, 21.07.2015 , RV “ Akademik M.A. Lavrentyev ”, cruise 71, Station 6–9, Agassiz trawl; collector I. Eidus.

Etymology. The species is named after the Russian ichthyologist G.U. Lindberg (1894–1976), initiator and author of the fundamental series “Fishes of the Sea of Japan and the adjacent parts of the Sea of Okhotsk and the Yellow Sea” in seven volumes ( Lindberg and Legeza 1959, 1965; Lindberg and Krasyukova 1969, 1975, 1987; Lindberg and Fedorov 1993; Lindberg et al. 1997).

Diagnosis. A snailfish with soft tissues of pelvic disk reduced. Vertebrae 53, D 51, A 42. Pectoral fin with 20–22 rays, notched; lower fin-lobe shorter than upper lobe. Mouth horizontal. Cephalic pores 2–6– 7–1. Pyloric caeca absent. Prickles on skin absent. Skin on head and body (where present) dark brown; peritoneum and branchial cavity black.

Description of the holotype. Counts provided in Table 1. Body deepest at nape, slim and gradually thinning towards the end. Head massive and rath- er large (length 3.8 in SL), deeper than it is wide (71.4 and 60.6% HL respectively). Occiput deep and swollen ( Fig. 1 ); dorsal contour depressed above eye. Snout blunt, not protruding, its length 1.8 times eye diameter. Orbit one-fourth of head length; eye 0.8 of orbit diameter, pupil round. Interocular 1.2 diameter of orbit. Nostril in front of lower half of orbit. Mouth horizontal, terminal; lower jaw not included. Maxillary reaching posteriorly to below center of eye. Teeth simple, not numerous (Table 1), in 4 oblique rows at each half of jaws, 5 and 4 teeth in a full oblique rows anteriorly on upper and lower jaw. Gill slit about onethird HL, longer than orbit and reaching ventrally to eighth pectoral fin ray. Opercular flap large, tip levels with pupil. Cephalic pores: 2 nasal, 6 infraorbital, 7 preoperculo-mandibular, and 1 suprabranchial. Preoperculo-mandibular pores large. Chin pores small and close together, but separate.

Precaudal part of body 2.7 in SL. Pleural ribs absent, epipleural ribs indistinguishable on radiographs. Pectoral fins not long (60% HL) and notched, right 22, left 20 rays. Upper pectoral lobes include 16 and 15 rays, lower lobes 6 and 5 rays accordingly. The upper pectoral ray about levels with mouth cleft; the longest rays reaching to sixth anal-fin ray. The lower fin-lobe not much long, reaching to 76% of the upper lobe length; tips of rays free of fin membrane. Disk skeletal, four pairs of pelvic rays are set apart, which is clearly visible through skin ( Fig. 1 , 3B ) and on radiogram. Disk large, 29% HL. Anus posterior to disk at a short distance, about one-fourth of disk length. Body not gelatinous. Skin thin, not prickled. Caudal fin broken. Color of skin on head and body (where present) is brown. Branchial cavity and peritoneum black.

Variability. Basic characters of paratypes are similar to those described (Table 1). Pyloric caeca absent (paratype ZMH 28702). The juvenile (ZMH 28671, about twice smaller than the holotype), has head and body lower and more compressed, predorsal and precaudal parts of body shorter, eye and orbit smaller; mandible to disk and to anus longer, but length from disk (and anus) to anal-fin origin shorter than larger specimen.

Morphometry. Holotype 92.6 mm SL (paratype ZMH 28671, 50.9 mm SL), in % SL: head length 26.0 (25.0), head depth 18.6 (13.9) and width 15.8 (12.2); maximum body depth 15.6 (11.6) and depth above anal-fin origin 9.1 (7.5); predorsal 26.1 (23.4) and pre-anal-fin length 36.5 (31.4); eye diameter 5.1 (3.5), gill slit 8.0 (7.7), mandible to pectoral-fin symphysis 8.0 (11.2); mandible to disk 13.1 (13.9) and to anus 21.6 (22.2); disk length 7.6 (9.4) and width 6.3 (5.7); disk to anus 1.9 (1.8) and to anal-fin origin 15.8 (9.8); anus to anal-fin origin 13.9 (8.1); length of upper pectoral lobe 15.7 (15.5), pectoral notch ray 5.2 (3.5) and lower pectoral lobe 11.9 (12.6); pectoral symphysis to anal-fin origin 25.2 (18.3). We cannot give measurements for paratype ZMH 28702 which is missing the last two or three vertebrae (SL 79+ mm).

Holotype (paratypes ZMH 28702 and ZMH 28671), in % HL: head depth 71.4 (65.1; 55.9) and width 60.6 (59.6; 48.8); maximum body depth 59.8 (56.0; 46.5) and depth above anal-fin origin 34.9 (39.4; 29.9); predorsal 100.4 (109.2; 93.7) and pre-anal-fin length 140.2 (130.7; 126.0); snout length 34.4 (35.3; 33.9), eye 19.5 (20.2; 14.2) and orbit diameter 24.5 (29.4; 22.0); postorbital length 46.1 (44.5; 53.5); interocular 28.6 (39.0; 27.6) and interorbital (bony) width 14.9 (13.3; –); upper jaw 43.6 (50.0; 44.9) and lower jaw length 53.5 (54.1; 56.7); width between corners of mouth 36.5 (52.3; 37.0), gill slit 30.7 (26.1; 30.7), disk length 29.0 (35.3; 37.8); upper pectoral lobe 60.2 (61.5; 62.2) and lower lobe 45.6 (41.3; 50.4).

Distribution. Type specimens are found in the Kuril Basin, an isolated abyssal plain in the southern part of the Sea of Okhotsk, at a depth of 3306 and 3348 m.

Comparisons. Three of the four species of the genus Osteodiscus live in regions remote from the place where the new species was captured, but one, O. andriashevi , described from the Sea of Okhotsk ( Pitruk and Fedorov 1990; Chernova et al. 2020, fig. 3) and recorded recently from Pacific waters of Japan (Iwate Prefecture), depth 1997–2108 m ( Murasaki et al. 2021b). Osteodiscus lindbergi differs from O. andriashevi in a notched pectoral fin (vs. fin almost unnotched, with rays gradually decreasing in length), in lower number of total vertebrae (53 vs. 55–60), dorsal and anal fin rays (51 vs. 52–54 and 42 vs. 46–49) ( Table 2), and head color (brown, including underside vs. ink black, Figs 3B, C ).

Osteodiscus lindbergi differs from O. abyssicola described off Hokkaido in the following different counts: total vertebrae 53 (vs. 49), dorsal fin rays 51 (vs. 44) and anal fin rays 42 (vs. 39). Gill slit is short- er in length (26–31% HL vs. 37%), but reaching to eighth pectoral ray (vs. to second ray); pelvic disk to anus shorter (1.8–7.5 vs. 15.5% HL) ( Murasaki et al. 2021a).

In O. cascadiae , described from Oregon waters ( Stein 1978), the first soft ray of pelvic disk is shifted forward close to the spine of subpelvic process and widely separated from remaining four soft rays, occupying the normal position (Kido, 1988: 151, fig. 14B). Disk of O. lindbergi similarly has only four pairs of rays together ( Fig. 3B ). Osteodiscus lindbergi is also close to O. cascadiae in meristic counts ( Table 2), but differs in having body lower (depth 15.4–15.5 vs. 15.9–23.3 % SL), pectoral-fin lower rays short- er (67–76 vs. 86–137% of upper-lobe length) and includes 5–6 rays forming a lobe (in O. cascadiae 3–5 rays closely set, with two of them threat-like – Fig. 4 ), prickles on skin absent (vs. present in males and females of all size, sitting in radiating clumps); teeth are fewer, forming 4 oblique rows at each half of jaws (vs. in narrow band of 18–24 oblique rows) ( Stein 1978: 25).

Osteodiscus lindbergi differs from O. rhepostomias (Bounty Trough, New Zealand vicinity) in having a horizontal (vs. oblique) mouth, numerous dorsal fin rays (51 vs. 46–47), a lower number of pectoral fin rays (20–22 vs. 24), and posterior position of anus (mandible to anus 80–83% HL vs. 68%) ( Stein 2012).

Figures

Fig. 1. Osteodiscus lindbergi sp. nov. Holotype ZMH 28701, female 92.6 mm SL, in lateral (top), ventral (middle) and dorsal view (bottom).

Fig. 2. Osteodiscus lindbergi sp. nov., paratype ZMH 28671, juvenile 50.9 mm SL, in lateral (top), ventral (middle) and dorsal view (bottom).

Fig. 3. Head region of Osteodiscus lindbergi sp. nov. (paratype ZMH 28671, juvenile 50.9 mm SL) in lateral (A) and ventral (B) views, and O. andriashevi (non type ZIN 49360, 151 mm SL) in ventral view (C). Pelvic disk with reduced soft tissue visible. Table 1. Counts of Osteodiscus lindbergi sp. nov., holotype and paratypes.

Fig. 4. Osteodiscus cascadiae (paratype OSIC 012771, 79 mm SL, off Oregon, depth 2850 m) in lateral (A, B), upper (C) and ventral (D) views.