Lestidiops ringens ( Jordan & Gilbert, 1880 (Jordan & Gilbert, 1880)

Ho, Hsuan-Ching & Yang, Tsung-Yu, 2024, Redescriptions of two Lestidiops species (Aulopiformes: Paralepididae) from Japan, with comments on their morphology, Zootaxa 5481 (1), pp. 30-42 : 34-39

Lestidiops ringens ( Jordan & Gilbert, 1880 )

Figs. 2B , 3 ; Tables 1‒2

Sudis ringens Jordan & Gilbert, 1880:273 (type locality: Santa Barbara Channel, California, U.S.A.; from stomach content).

Lestidiops ringens ( Jordan & Gilbert, 1880): Rofen 1966: 304, 322 (mention). Post 1972:159 (type catalog). Materese et al. 1989:134 (early stages). Amaoka et al. 1992: 8 (early stages): Moser et al. 1993:112 (larval distribution). Ambrose in Moser 1996:360 (early stages). Materese et al. 2003:96 (larval distribution). Fukui & Ozawa 2004:293 (list). Mundy 2005:204 (list). Okamoto et al. 2006:78 (description). Nakabo 2013:441 (key).

Specimens examined. NSMT-P 58834 (1, 208), 39°59'30"N, 144°54'36"E, Iwate, Honshu , northern Japan, mesopelagic trawl, 220‒470 m, 15 Jul. 1996 . NSMT-P 58851 (1, 243, nape broken), 40°01'54"N, 144°58'24"E, Iwate, Honshu , northern Japan, mesopelagic trawl, 630‒657 m, 15 Jul. 1996 . NSMT-P 58940 (1, 98), 39°01'36"N, 143°30'24"E, Miyagi-Iwate , Honshu, northern Japan, mesopelagic trawl, 550‒578 m, 30 Jul. 1996 . HUMZ 85089 (1, 202), 44°29'36"N, 170°19'18"E, Suiko Sea Mount , Emperor Seamount Chain, 1127 m, 21 Jul. 1979 . HUMZ 141303 (1, 241), Pacific coast off Tohoku, Japan, bottom trawl, 6 Sep. 1995 . HUMZ 166717 (1, 212), Pacific coast off Hokkaido, Japan, 1 Sep. 1999 . HUMZ 222604 (1, 237), off Tohoku, bottom trawl, 752 m, 3 Nov. 2013 .

Diagnosis. A species of Lestidiops with lateral line complete, running to caudal- fin base; body moderately long; anus slightly behind tip of appressed pelvic fin; head and snout short and blunt; vertebral counts: PVV 31‒32, PDV 41‒42, PHV 45‒46, PAV 58, TV 90‒92; lateral-line scales: PVLL 31‒33, PDLL 41‒43, PALL 60‒62, TLL 131‒138.

Description. Morphometric and meristic data are provided in Tables 1‒2 . Dorsal-fin rays 13; pectoral-fin rays 12–13; pelvic-fin rays 9; anal-fin rays 27‒29. Lateral-line scales: PVLL 31‒33, PDLL 41‒43, PALL 60‒62, TLL 130‒138, including 68‒73 large scales and 60‒70 small ones on posterior portion. Vertebral counts: PHV 45‒46; CV 44‒45; PVV 31‒32; PDV 41‒42; PAV 58, and TV 90-92.

Body relatively slender, rather compressed, depth at pectoral fin 12‒21 in SL. Caudal peduncle long, its length 1.2‒1.7 times eye diameter ( Figs. 3A, B ). Ventral adipose fin absent from both abdominal ridge between pectoral and pelvic fins and margin between anus and anal fins. Anus situated slightly to clearly behind tip of appressed pelvic fin, about 0.3‒1 pelvic-fin length behind the fin tip; anus closer to DFO rather than VFO or at around middle of D‒V; distance from VFO to anus about 3.7‒4.7 times in V‒A ( Fig. 3C ).

Head relatively short and stout, its length 5.1‒5.9 in SL; snout short and blunt anteriorly, its length 2.0‒ 2.2 in HL ( Fig. 3D ). Mouth terminal, relatively small, its gape extending to slightly less than one eye diameter in front of eye. Lower jaw slightly upturned at tip, with small distal tab of fleshy tissue. Eye large, its diameter 3.7‒4.8 in HL. No light organ around eye. First suborbital bone slender, fifth and sixth bones not expanded posteriorly, and seventh moderately large.

Interorbital space narrow, its width 6.8‒7.5 in HL; some smooth ridges present on top of head and snout. Two nostrils situated at slightly less than 1 eye diameter before the eye, well in front of posterior end of premaxilla and slightly behind midpoint of snout. Maxilla short, extending nearly to anterior margin of eye, to a vertical about 1/8 eye diameter before the eye margin. Sensory canals on snout, cheek, operculum, and jaws, not clearly visible in most specimens due to lost skin; numerous sensory pores on dorsal surface of snout and lower surface of lower jaw.

Gill filaments present on all four gill arches. Fourth arch mostly connected to gill chamber wall by membranes. Pseudobranchs present, anterior half included in a deep pocket.

DFO situated at about posterior two-fifths of the fish, well behind VFO but closer to VFO than AFO, predorsal length 1.6‒1.7 in SL. Pectoral-fin base slightly behind posterior margin of gill cover, upper end of fin base about at a horizontal line drawn through lower margin of eye; no small pocket behind fin base. VFO at about midpoint of the fish, pre-pelvic fin length 1.9‒2.1 in SL. Anus clearly behind tip of appressed pelvic fin, by about 1/3 to 1 pelvic-fin length. A tiny axial scale behind pelvic-fin base. Anal fin originating in posterior fourth of fish, pre-anal length 1.2‒1.3 in SL. Dorsal adipose fin over rear portion of anal-fin base, its base length slightly smaller than eye diameter.

Two or three small fangs at tip of upper jaw, followed by single row of small, retrorse teeth, these gradually becoming smaller on posterior part of jaw. Vomerine teeth absent. One to three fangs (either depressible or fixed) at front end of each lower jaw, followed by two rows of small fangs arranged in about 7 or 8 pairs; those of inner row very long with knife-like tip and depressible; those in outer row much shorter (about 1/ 4 in length of the adjacent inner teeth), curved, and fixed. Two rows of fangs on each palatine with anteriormost teeth arranged in 3‒5 (usually 3) pairs, those in inner row long and depressible, on outer row small and fixed, followed by single row of small, fixed teeth on posterior half of palatine. No or few small teeth on tongue, some teeth at middle forming two short rows and some restricted on posterior portion of tongue.

Relatively few gill rakers on gill arch, rather loose in arrangement. Narrow, shield-shaped gill rakers present on epibranchial, ceratobranchial, and hypobranchial parts of each gill arch, each raker usually with 1 or 2 (rarely 3 or more) slender teeth on broad base, these teeth extending slightly upward beyond margin of gill arch. Slender teeth on pharyngeal arch arranged in an oval patch with about 5 or 6 rows in middle. Single row of small teeth on fifth ceratobranchial.

Body scaleless, except for single row of complete lateral-line scales extending from above pectoral girdle to caudal-fin base. Lateral-line scales longer than tall, gradually becoming narrower (as wide as deep) posteriorly, with many strongly reduced scales on posterior portion; 1 large pore on each upper and lower margin of all scales.

Luminescent duct absent.

Size. Largest specimen examined is 243 mm SL, sex indeterminate.

Coloration ( Figs. 3A, B ). Body generally light brown, with some specimens exhibiting a green metallic shine. Upper fifth of body light brown with tiny melanophores and large unpigmented areas behind the eye and on the lower portion of the body. Melanophores on the dorsum do not extend downward to the lateral line, leaving an unpigmented area above the lateral line before the DFO; melanophores gradually extend below and cover the lateral line behind the DFO.

Head loosely covered by melanophores, with denser concentrations on the tips of the snout and lips of the lower jaw, the dorso-posterior corner of the orbit, and a large black patch on the top of the skull. A narrow, wavy band of melanophores is present beneath skin along the upper margin of lateral line, with a few scattered dots along the lower margin of anterior third of lateral line, gradually becoming denser and forming a wavy line posteriorly. Lower half of the body mostly without melanophores. Row of small dots along ridge between the anus and the anal fin, with the caudal peduncle displaying dense melanophores.

Upper pectoral fin rays, outer rays of pelvic fin, and all rays of dorsal, anal, and caudal fins covered with melanophores. Peritoneal membranes dark brown, and mouth cavity and gill chamber mostly pale, with the inner surface of operculum covered with loose melanophores.

A 96.1 mm SL specimen has less pigmentation on the body, but there are dense melanophores along the upper margin of the lateral line.

Distribution. Only a few records of adults from the northern Pacific Ocean, off Japan (ca. 39‒ 40°N) (this study), Kuril Islands ( Parin et al., 1995), but rather common in the northeastern Pacific Ocean (ca. 22‒ 59°N) ( Fig. 2B ). Bathymetric range 220‒752 m in Japan. Based on collected specimens, L. ringens is quite abundant in the northeastern Pacific Ocean, although most are larvae and juveniles, compared to those in the northwestern Pacific Ocean (this study; also see http://www.fishnet2.net/).

Remarks. A small specimen (96.1 mm SL) has most posterior small scales lost and no trace can be detected. This is not a common situation, because when the scales are lost, usually pockets or a canal remain. However, the specimen has almost identical vertebral formula and is thus recognized as the same species.

Figures

FIGURE 2. Distribution maps of two Lestidiops species. A. L. sphyraenopsis Hubbs, 1916. B. L. ringens (Jordan & Gilbert, 1880), the distribution range in northeastern Pacific is shaded with stipple. Solid symbol represents the holotype of each. One symbol may represent more than one capture.

FIGURE 3. Lestidiops ringens (Jordan & Gilbert, 1880) HUMZ 222604, 237 mm SL, off Tohoku, Japan. A. Fresh, photo by HUMZ. B‒D. preserved, anterior to right. B. lateral view. C. Lateral view of mid-trunk showing origins of dorsal, pelvic and anal fins (bars). D. Lateral view of head. Arrow points to the anus.