Lycenchelys ryukyuensis Shinohara & Anderson, 2007

Kawarada, Shumpei, Imamura, Hisashi, Narimatsu, Yoji & Shinohara, Gento, 2020, Taxonomic revision of the genus Lycenchelys (Osteichthyes: Zoarcidae) in Japanese waters, Zootaxa 4762 (1), pp. 1-66 : 42-45

Lycenchelys ryukyuensis Shinohara & Anderson, 2007

(Japanese name: Ryukyu-hebigenge)

( Figs. 36–37 ; Table 9)

Lycenchelys ryukyuensis Shinohara & Anderson, 2007: 59 , figs. 1–3, table 1 (original description, type locality: Okinawa Trough, Ryukyu Islands, East China Sea, Japan); Hatooka, 2013: 1225, 2078, unnumbered fig. (key to species); Nakabo & Hirashima, 2015: 216 (species list and etymology of scientific name).

Materials examined

Holotype: NSMT-P 63965, male, 159.3 mm SL, Okinawa Trough, eastern Ryukyu Islands, East China Sea (26°11.34’N, 124°54.27’E to 26°12.65’N, 124°55.47’E), 1493–1533 m depth, 26 Apr. 2002, R/V Tansei-maru, beam trawl.

Paratypes (2 specimens): NSMT-P 63966–67, 2 females, 116.9–142.6 mm SL, collected with holotype.

Diagnosis. Vertebrae 22–24 + 96–102 = 118–124; head length 14.1–14.4% SL; intertorbital pores and occipital pores absent; postorbital pores usually 3; suborbital pores 6 + 1–2; preoperculomandibular pores 8; vomerine teeth 2–4; palatine teeth 1–2, arranged in single row; opercular flap well developed; pelvic-fin base positioned anterior to lower edge of gill opening; lateral line complete and positioned ventrally; scales absent on pectoral fin and its base; body uniformly grayish brown when fresh.

Description. Counts and proportional measurements in Table 9.

Body very elongate, cross section oval anteriorly, compressed laterally near tail; its width at anal-fin origin 3.4–4.0 (3.4)% SL. Head moderately short, oval, dorsal profile of head gently sloping to above pectoral-fin base. Snout short, 133.7–149.7 (149.7)% of eye diameter. Eye ovoid, relatively small. Interorbital space narrow, width 19.7–22.9 (19.7)% of eye diameter. Nostril tube short, not reaching upper lip when depressed. Mouth subterminal. Posterior edge of upper jaw reaching to about vertical through middle of eye in adult male (holotype), reaching to below anterior margin of eye in females (2 paratypes). Labial lobe of lower jaw reduced. Teeth on jaws, vomer and palatine small and conical; upper jaw with 2–3 rows anteriorly and 1–2 rows posteriorly; lower jaw with 2–3 irregular rows anteriorly and 1–2 rows posteriorly; vomerine teeth irregularly arranged; palatine teeth in single row. Lower edge of gill opening about level with lower end of pectoral-fin base. Opercular flap well developed. Gill rakers short and triangular. Pseudobranch filaments extremely short. Lateral line deciduous. Scales small and cycloid, present on body, tail and about basal half of vertical fins. Head, nape, pectoral fin and its base lacking scales.

Dorsal-fin origin above middle of pectoral fin; 1st dorsal-fin pterygiophore between neural spines of 7th and 8th vertebrae. Anal-fin origin below 15th or 16th (15th) dorsal-fin ray; 1st anal-fin pterygiophore posterior to parapophysis of ultimate abdominal vertebra. Last dorsal-fin pterygiophore between neural spines of 3rd to 5th (between 4th and 5th) preural vertebrae. Last anal-fin pterygiophore between hemal spines of 3rd to 5th (between 4th and 5th) preural vertebrae. Caudal fin with 2 epural, 4–5 (4) upper hypural and 3 lower hypural rays. Pectoral fin moderately short, reaching to about middle of abdomen; its posterior margin rounded dorsally and notched ventrally. Upper end of pectoral-fin base on about lateral midline of body. Pelvic fin short; its base posterior to lower edge of gill opening; its posterior margin reaching lower edge of gill opening.

Head pores well developed and distinct. Nasal pores 2; anterior pore in front of nostril tube, posterior pore above 1st suborbital pore ( Fig. 37A, B ). Postorbital pores 3 ( Fig. 37A, B ); distance between 1st and 2nd pores longest of those between adjacent pores. Suborbital pores 7 or 8 (7); 6 pores below eye and last 1 or 2 (1) pore(s) on ascending part of suborbital canal behind eye; 6th pore behind vertical through posterior margin of eye ( Fig. 37A ). Preoperculomandibular pores 8; 4 on lower jaw and 4 on preopercle; last preoperculomandibular pore posterior to lower margin of eye ( Fig. 37A, C ). Interorbital pores and occipital pores absent ( Fig. 37B ).

Color in alcohol. Holotype ( Fig. 36 ; lacking body skin) with dark brown head and pectoral fin, flesh colored body, grayish vertical fins, and pale brown margins on vertical fins.

Color when fresh [based on color photograph in Shinohara & Anderson (2007)]. Head and pectoral fin blackish, body grayish, and margins of vertical fins dark brown.

Distribution. East China Sea off the eastern Ryukyu Islands and in the Okinawa Trough, at depths of 991–1533 m ( Shinohara & Anderson, 2007; Hatooka, 2013; this study).

Size. Maximum length 17 cm TL ( Hatooka, 2013). The largest specimen examined during this study measured 159.3 mm SL (161.6 mm TL).

Remarks. Shinohara & Anderson (2007) compared L. ryukyuensis with Lycenchelys aratrirostris Andriashev & Permitin, 1968 , Lycenchelys bellingshausenni Andriashev & Permitin, 1968 , Lycenchelys folletti Anderson, 1995 , Lycenchelys lonchoura Anderson, 1995 and Lycenchelys maoriensis Andriashev & Fedorov, 1986 . Although L. ryukyuensis is similar to these species in sharing a combination of five characters (no interorbital pores and occipital pores, usually 3 postorbital pores, presence of pelvic fins and a single ventrally positioned lateral line; Shinohara & Anderson, 2007), it is distinguishable from L. aratrirostris , L. bellingshausenni , L. folletti and L. lonchoura in having higher numbers of dorsal- and anal-fin rays, and total vertebrae (110–114, 98–104 and 118–124, respectively, in L. ryukyuensis vs. 97–107, 79–89 and 101–110 in L. aratrirostri , 94–103, 82–91 and 102–110 in L. bellingshausenni , 97–104, 83–92 and 102–109 in L. folletti , and 103, 86 and 107 in L. lonchoura ), and from L. maoriensis in having 7–8 suborbital pores and no black or brown variegations along the body and tail in males (vs. 6 suborbital pores and black or brown variegations present in L. maoriensis ) ( Shinohara & Anderson, 2007). On the other hand, Lycenchelys polyodon Anderson & Møller, 2007 also has the above-mentioned combination of 5 characters, but has not been compared with L. ryukyuensis . The two are difficult to separate on the basis of numbers of dorsal- and anal fin-rays, total vertebrae and suborbital pores (113, 105, 123 and 7, respectively, and no variegations on the body and tail in L. polyodon ) ( Table 9). However, L. ryukyuensis is clearly distinguished from L. polyodon in having considerably lower numbers of vomerine and palatine teeth (2–4 and 1–2 in L. ryukyuensis vs. 26 and 31–33 in L. polyodon ) ( Table 9).

Figures

FIGURE 36. Lycenchelys ryukyuensis, NSMT-P 63965, holotype, 159.3 mm SL, in alcohol.

FIGURE 37. Lycenchelys ryukyuensis, NSMT-P 63965, holotype, 159.3 mm SL, male, views of head showing positions of head pores. (A) Lateral, (B) dorsal and (C) ventral.