Stemonosudis retrodorsalis, Ho & Russell & Graham & Psomadakis, 2019

Ho, Hsuan-Ching, Russell, Barry, Graham, Ken & Psomadakis, Peter N., 2019, Review of the Stemonosudis rothschildi species complex, with descriptions of two new species from the Indo-west Pacific Ocean (Aulopiformes: Paralepididae), Zootaxa 4702 (1), pp. 216-229 : 225-228

Stemonosudis retrodorsalis sp. nov.

Back-fin barracudina

Figs. 2C , 4–5 ; Tables 1–2

Stemonosudis rothschildi (non Richards): Post, 1982:29 (description; Indonesia). Gloerfelt-Tarp & Kailola, 1984:79 (figure; Indonesia).

Holotype. BSKU 15795 (151 mm SL), R/ V Hakuho-maru, KH-72-01, sta. 20, 5°40.9’N, 119°46.3’E– 5°43.1’N, 119°47.0’E, off Tawitawi Island, the Philippines, Sulu Sea , 460–514 m, 30-foot otter trawl, 10 Jun. 1972, coll. O. Okamura.

Paratypes. BSKU 15794 (1, 161 mm SL) , BSKU 15796–15802 (8, 100–142) , NMMB-P30958 (3, 111–137) , all collected together with the holotype. BMNH 1981.11 . 30.1 (1, 146.4), 8°44’S, 114°16’E southern coast of eastern Java, Indonesia, 40–180 m, midwater trawl, 15 Jul. 1979 [ Fig. 4D ; detailed description provided in Post, 1982] .

Non-type. AMS I.26000-001 (1 of 5, 146), FRV Soela, sta. So 2/82/43,45, 18°44’S, 117°02’E, 210 km north west of Port Hedland, Northwest Shelf, Eastern Indian Ocean, 396–406 m, Engel trawl, 13 Apr 1982, coll. J. Paxton & M. McGrouther.

Diagnosis. A species of the S. rothschildi species complex with dorsal fin situated far posteriorly, at about vertical through AFO; preanal length 73.2–79.9% SL; six saddles on dorsum before dorsal fin; four saddles on abdomi- nal ridge before pelvic fin; V–D 96.3–105.3% V–A; vertebrae before DFO 57–58, before AFO 56–58; vertebrae between VFO and DFO 17–19; lateral-line scales before DFO 56–68 and before AFO 57–58.

Description. Holotype first, paratypes and non-types in brackets after. Dorsal-fin rays 10 (9–10, usually 10); pectoral-fin rays 13 (12–13); pelvic-fin rays 9; anal-fin rays 34 (32–34). Lateral-line scales: PVLL 40 (39–41); PDLL 58 (56–58); PALL 57 (57–58); and total 77 (75–77), including 7 (3–7) smaller scales on posterior end. Ver- tebral counts: 42 (42–43) prehaemal; 48 (46–49) caudal; 39 (38–40) prepelvic; 58 (57–58) predorsal; 57 (56–58) preanal and 90 (89–91) in total.

Body moderately elongate and strongly compressed, body depth at pectoral-fin base 19 (17–28) times in SL; ventral profile of belly nearly straight; greatest depth of body at approximately middle of body. Caudal peduncle short, slightly less than the eye diameter. Well-developed, moderately narrow ridge between head and pelvic fins. Anus above tip of the appressed pelvic fin, well in front of DFO.

Head moderately slender, slightly wider at opercles than the maximum body width. Snout moderately long and pointed distally. Mouth terminal, moderately large, extending beyond anterior margin of eye; tip of lower jaw slightly upturned, with small blunt fleshy tip. Postorbital head length less than half of head length. Eye round, diameter 5.8 (5.5–6.0) in HL. No light organs in front of or on lower margin of eye. Interorbital flattened, width 8.2 (7.7–8.6) in HL, with two lateral, compressed, longitudinal ridges on each side.

Two nostrils close together, slightly but clearly before posterior end of maxilla, about 0.8 eye diameter before eye. Upper jaw length 2.1 in HL, maxilla terminating about one-third eye diameter before a vertical through anterior margin of eye. Opercle thin, with posterior margin bluntly pointed, its lower margin slightly notched around base of pectoral fin. Gill membranes joined far forward, before vertical from anterior margin of eye, free from isthmus. Numerous sensory canals on snout, check, operculum, and jaws; numerous sensory pores on dorsal surface of snout and lower surface of lower jaw.

Pectoral fin slender, originating about level of lower margin of eye, slightly behind vertical through posterior margin of gill cover. Small pocket behind pectoral-fin base. DFO at about 1/5 SL before caudal fin, at about vertical through AFO (slightly before or behind in some). VFO well before vertical through DFO. Very small axial scale, mostly embedded, behind pelvic-fin base. Dorsal adipose fin above rear portion of anal-fin base. Ventral adipose fin moderately developed on abdomen ridge, wall-developed between margin of anus and AFO.

Premaxilla with 2 or 3 (usually 3) small depressible canines, followed by row of many small, closely-spaced, fixed, retrose teeth along upper jaw, gradually smaller posteriorly. Vomerine teeth absent. Mandible with 2 or 3 short fixed teeth at front, then small toothless gap, followed by two rows of large broadly-spaced teeth forming 7 or 8 pairs; teeth in inner row long, depressible, each with knife-like tip; in outer row short and fixed. Palatine with 2 rows of canines anteriorly forming 6 or 7 widely-spaced pairs, teeth in outer row small and fixed, followed by single row of short, fixed retrose teeth, in inner row long and depressible. Tongue fleshy, spatulate anteriorly, with two parallel longitudinal rows of teeth extending length of glossohyal, each row with 10–12 small teeth. Basihyal without teeth.

Gill rakers ( Fig. 2C ) somewhat rudimentary and not easy to observe without staining; well developed in outer the two arches and poorly developed on the two inner arches. Each raker with 2 or 3 (mainly 2) short teeth. First arch with 3 small rakers on epibranchial, 15 on ceratobranchial, and several on posterior half of hypobranchial, those on anterior half with their bases fused to each other ( Fig. 2C ). Single row of small teeth on fifth cerotobrachial. Four gill arches, filament present on the first to fourth arches. The fourth mostly connected to the gill wall by membrane. Pseudobranches present, inside a deep pocket above first gill arch.

Body devoid of scales, except for lateral-line scales originating from above pectoral girdle and running to above about posterior third of anal-fin base. Anterior lateral-line scales slightly wider than high, gradually becoming smaller and becoming narrower posteriorly; those in anterior half of lateral line with concave on upper and lower margins; each scale with 3 pores above and below the posterior portions, the anteriormost one largest; posterior scales with only 1 pore in general.

No luminescent duct in abdominal cavity. Peritoneal sections well developed and clearly separated in adults.

Coloration. Fresh coloration translucent with similar, but much paler pigmentation than in preservation ( Fig. 4D ). Coloration of preserved specimens ( Figs. 4–5 ) with dorsal half of body generally brownish, with relatively large and scattered chromatophores and darker saddles consisting of numerous tiny and dense chromatophores. Ventral half of body mostly devoid of pigment, except for blotches similar to dorsal surface and a narrow stripe of chromatophores on submargin of abdominal ridge.

Anterior half of snout and lower jaw densely covered with chromatophores, somewhat blackish; other parts of head with unevenly and loosely scattered chromatophores. Top of head brownish. All fins blackish, except for pale pectoral fin sometimes with few chromatophores.

Dorsal saddles alternating with ventral saddles before AFO. Eight saddles on dorsum, 4 before VFO, fifth slightly before midpoint of V–A, sixth just in front of DFO, 7th relatively wide, above about middle of anal fin base, posterior portion connected to 8th saddles of ventral margin, and last fused with ventral saddle, forming broad band.

Nine saddles on ventral margin; 4 on abdomen before VFO, 5th at pelvic fin base; 6th at midpoint of V–A, 7th right at anterior quarter of anal-fin base, its base much longer than others; 8th right above posterior 1/3 of anal-fin base; and the last on caudal peduncle, fused with the last saddle of dorsum, forming a wide band.

Peritoneal membranes divided into 11 sections, 1st at pectoral-fin base; 8 between pectoral and pelvic fins, 1 at pelvic fin base and 1 behind pelvic fin base.

Size. The largest specimen examined in this study is 161 mm SL.

Distribution. Known from eastern Indian and western Pacific oceans off the Philippines (Sulu Sea; Western Pacific Ocean), eastern Java, Indonesia and Northwest Shelf of Australia. Specimens were collected by bottom trawl at continental slope (396–514 m), except for one collected by mid-water trawl (40–180 m) at night.

Etymology. The specific name is combination of retro means behind and dorsalis mean back, here the dorsal fin, in referring to the backward position of dorsal fin.

Remarks. Stemonosudis retrodorsalis sp. nov. is unique for the family in having the dorsal fin originated far back, at about same vertical as AFO. It is most similar to S. rothschildi in coloration, body proportions, and fin and vertebral formulae. Characters related to the backward position of dorsal fin are V–D = 96.3–105.3% V–A (vs. 64.3–73.1%); vertebrae before DFO 57–58 (vs. 50–53); lateral-line scales before DFO 56–68 (vs. 50–52); vertebrae between VFO and DFO 17–19 (vs. 9–12). It is notable that the predorsal length of both species are strongly over- lapped, but the preanal length is relatively short in S. retrodorsalis (73.2–79.9% SL; vs. 79.1–80.0%), so that the position of the anal fin in S. retrodorsalis is relatively forward compared to that of S. rothschildi .

Other useful characters that distinguish S. retrodorsalis from S. rothschildi are smaller head, length 16.8– 19.1% (vs. 19.7–22.4% SL); larger eye, diameter 16.5–18.3% HL (vs. 12.7–15.5% HL), a broader interorbital width 11.7–13.0% (vs. 8.7–11.4% HL); a shorter snout, length 8.9–10.3% SL (vs. 11.2–11.6% SL) and 51.3–53.9% HL (vs. 53.5–57.5% HL); and both jaws relatively short, upper jaw 8.2–9.3% SL (vs. 9.9–10.8% SL) and lower jaw 11.1–12.0% SL (vs. 12.8–13.5% SL).

Figures

FIGURE 2. First gill arch and its rakers of three Stemonosudis species. A. S. rothschildi, NMMB-P39061, 176 mm SL. B. S. multifasciata sp. nov., NMMB-P30956, paratype, 247 mm SL, arrow indicates the rudimentary rakers. C. S. retrodorsalis sp. nov., from the holotype, arrow indicates the fused rakers. Anterior to right; not to scale.

FIGURE 4. Stemonosudis retrodorsalis sp. nov., A–C. holotype, BSKU 15795, 151 mm SL. A, Lateral view. B. Lateral view of trunk, anterior to left. C. Lateral view of head (reversed). D. BMNH 1981.11.30.1, 146.4 mm SL, photo by T. Gloerfelt-Tarp. Arrows indicate the DFO (above), VFO (lower left) and AFO (lower right). Anterior to left.

FIGURE 5. Stemonosudis retrodorsalis sp. nov., BSKU 15800, 105 mm SL.A. Dorsolateral view. B. Lateral view of trunk. C. Ventral view showing ventral saddles on abdominal ridge, lines indicate the saddles. Arrows indicate the DFO (above), VFO (lower left) and AFO (lower right).