Lestidiops extremus ( Ege, 1953 )

Ho, Hsuan-Ching & Huang, Chih-Hsiung, 2022, First adult record of the barracudina Lestidiops extremus (Ege, 1953), based on a specimen from the Philippines (Teleostei: Paralepididae), Zootaxa 5195 (6), pp. 579-584 : 580-582

Lestidiops extremus ( Ege, 1953)

Figure 1 ; Table 1

Lestidium extremum Ege, 1953: 136 , fig. 29

(type locality: Molucca Passage, 0°18′S, 132°52′ E [West Papua, Indonesia], ca. 100 m). Post, 1972: 147 (type catalog; in Lestidiops , but possibly referable to Uncisudis ).

Lestidiops extremus ( Ege, 1953) : Rofen, 1966:301 (listed). Paxton & Niem, 1999: 1949 (listed). Fukui & Ozawa, 2004: 293 (listed).

Material examined. Holotype of Lestidium extremum: ZMUC P 2316999 (21.8 mm SL), 0°18′S, 132°52′E, West Papua, Indonesia, ca. 100 m, 29 Jul. 1929. Non-type. AMS I.36462-006 (sex undetermined, 190 mm SL), about 80 km NW off Camarines Norte Province, southeastern Luzon , the Philippines, 14°50.46′N, 123°17.30′E –14°47.35′N, 123°22.33′E, otter trawl, 760–770 m, 27 Sep. 1995, coll. J. Paxton & party.

Diagnosis. A species of Lestidiops with VFO clearly behind DFO, also slightly behind posterior end of dorsalfin base; anus well behind DFO; posterior end of maxilla extending nearly to vertical drawn through anterior margin of eye; 33 predorsal, 39 caudal and 80 total vertebrae; 10 or 11 dorsal-fin and 31–33 anal-fin rays; adult body uniformly dark brown.

Observations of holotype. Coloration mostly lost. VFO slightly but clearly behind posterior end of dorsalfin base. Anus directly above tip of adpressed pelvic fin, situated at about midpoint of distance between origins of dorsal and anal fins. Ventral adipose fin well developed.

Posterior end of maxilla almost directly below anterior margin of eye. Nostrils well in front of posterior end of maxilla, about 0.8 times eye diameter before anterior margin of eye. Gill rakers not developed and lateral-line scales not visible. Duct clearly visible along ventral margin of abdominal cavity, apparently not intestine.

Description of adult. Dorsal-fin rays 10; pectoral-fin rays 12; pelvic-fin rays 10; anal-fin rays 31; lateral line with 34 scales before DFO, 38 scales before VFO, 51 before AFO and 71 in total, with 63 large scales plus 8 small scales in rear portion. Vertebrae: predorsal 33, prepelvic 38, preanal 50, prehaemal 41, caudal 39, total 80. Gill rakers: 9 on upper limb (epibranchial) and 25 on lower limb, including 15 on ceratobranchial + 10 on hypobranchial.

Body moderately long, strongly compressed, depth at pectoral fin 6.8% SL. Caudal peduncle moderately long, 1.6 times eye diameter. Ventral adipose fin very weakly developed along abdominal ridge between pectoral and pelvic fins, slightly better developed on margin between pelvic and anal fins. Anus above tip of appressed pelvic fin, slightly but clearly behind dorsal-fin base and situated at midpoint of V–A.

Head short, its length 21.4% SL; snout blunt, its length 50.1% HL. Mouth terminal, moderately large, with gape extending to about middle of eye; lower jaw slightly upturned at tip, with small distal tab of fleshy tissue. Eye small, its diameter 17.0% HL. No light organ around eye. First suborbital bone slender, fifth and sixth expanded posteriorly, and seventh small. Interorbital space narrow, its width 12.3% HL; some straight ridges present on top of head and snout. Posterior end of maxilla extending nearly to vertical drawn through anterior margin of eye. Two nostrils located well in front of posterior end of maxilla, about 0.8 eye diameter in front of eye. Numerous sensory canals on snout, cheek, operculum and jaws; 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 membrane. Pseudobranchs present within deep pocket.

DFO well behind midpoint of fish and well in front of VFO, predorsal length 57.9% SL. Pectoral-fin base even with posterior margin of gill cover, upper end of fin base slightly below horizontal drawn through lower margin of eye; no small pocket behind fin base. VFO slightly but clearly behind posterior end of dorsal-fin base, pre-pelvic fin length 63.2% SL. No axial scale behind pelvic-fin base. Anal fin originating in posterior fourth of body, preanal length 76.1% SL. Distance between VFO and AFO relatively short, 12.9% SL. Adipose fin above rear portion of anal-fin base.

Two small fangs at tip of upper jaw, followed by single row of numerous small, retrorse teeth, these gradually become smaller on posterior part of jaw. Vomerine teeth absent. Two depressible fangs at front of each lower jaw, followed by two rows of fangs arranged in 12 (right) or 5 (left) pairs; those of inner row long with knife-like tip and depressible; those in outer row much shorter, curved back and fixed, slightly embedded in tissue. Two rows of fangs on each palatine, anterior teeth forming 5 widely-spaced tooth pairs, those in outer row long and depressible, those in outer row small and fixed; these fangs followed by single row of small, widely-spaced fixed teeth on posterior part of jaw. One row of small, straight teeth present on each side of tongue.

Gill rakers present on epibranchial, ceratobranchial, and hypobranchial parts of each gill arch, shield-shaped, each with 2–5 (mostly 3 or 4) small teeth and broad base. Teeth on pharyngeal arch short, forming oval patch, with about 4 rows in middle. Single row of small teeth on fifth ceratobranchial.

Body scaleless except for single row of lateral-line scales originating from above pectoral girdle and running to point above about two-thirds length of anal-fin base. Lateral-line scales slightly longer than wide, gradually smaller and narrower posteriorly; 1 large pore on margin of each scale, accompanied by 2–3 tiny pores.

Luminescent duct absent.

Coloration. Body of adult uniformly dark brown with ventral margin distinctly darker; mouth cavity and gill chamber black; anterior portion of tongue pale; peritoneal membranes of abdominal cavity black with silvery-white groove along ventral margin (this study). Body of juveniles pale with black saddles on dorsum and broad black bands on caudal region, also with 7–11 clear peritoneal sections ( Ege, 1953).

Distribution. Formerly known only from the type series collected off the Bird’s Head Peninsula, West Papua, Indonesia, ca. 100 m; newly recorded from much deeper water in seas east of Luzon Island, Philippines, 760–770 m, which may suggest a depth shift in adults.

Comparison. The present adult specimen differs from adults of L. mirabilis , the only other congener with VFO behind DFO, in having the VFO slightly but clearly behind the posterior end of the dorsal-fin base (vs. below about middle of the dorsal-fin base); V–A relatively short at 12.9% SL (vs. 15.2–17.1% SL), 31–33 anal-fin rays (vs. 28–30 rays); 39 caudal vertebrae (vs. 44 or 45); 80 total vertebrae (vs. 86); and 34 total gill rakers (vs. 61, n=1) ( Table 1 ).

Figures

FIGURE 1. A–C. Adult specimen of L. extremus, AMS I.36462-006, 190 mm SL. A. Lateral view. B. Lateral view of head, arrow points to the nostrils and bar indicates the posterior end of maxilla. C. Lateral view of posterior half of body, with red bars indicating end of dorsal-fin base (upper), VFO (lower right), and AFO (lower left), and arrow indicating rear end of lateral line. D. Original drawing of holotype, reproduced from Ege (1953).