Stemonosudis siliquiventer Post, 1970

Ho, Hsuan-Ching & Yang, Tsung-Yu, 2025, A new barracudina (Aulopiformes, Paralepididae, Stemonosudis) from Somalia, with additional records of S. siliquiventer from the Caribbean Sea, ZooKeys 1241, pp. 93-104 : 93-104

Stemonosudis siliquiventer Post, 1970

Figs 2 , 3 , Tables 1 , 2 , 3

Stemonosudis siliquiventer Post, 1970: 205, figs 1–5 (Atlantic, 3°00'S, 26°16'W, depth 2000 meters). Fukui and Ozawa 2004: 293 (listed). Ho et al. 2019 a: 17 ( Taiwan, redescription of adults). Eduardo et al. 2022: 7 ( Brazil, 1 specimen).

Original description.

Post (1970) described this species based on the holotype (159.5 mm SL), 5 paratypes (25.6–105.5 mm SL), and 7 non-types (58 + – 93.5 mm SL). These specimens were collected from a broad area around the central western Atlantic Ocean (Fig. 3 ). Except for two specimens (Table 1 ), all other specimens are juveniles smaller than 100 mm SL.

The following diagnosis is translated directly from the original description in German ( Post 1970), however, based on our observation, most of the characters are general for all species of Stemonosudis : “ Body elongate, slender, higher than wide; ventral muscular carina present between pectoral and pelvic fins; head short, more than 5 times in SL; snout ca. 1 / 2 of head length; anterior edge of nostril at one eye diameter in front of eye; nostrils above posterior edge of premaxilla; eye moderately large, ca. 1 / 2 of head depth; lower jaw hinged under center of the eye, with a non-ossified process at the tip; fins not especially elongate; pelvic and dorsal fins behind middle of body, dorsal fin behind pelvic fin; dorsal-fin base over the middle of space between V – A; post-dorsal length ca. 1 / 3 of SL; anus at middle between V – D; adipose fin above last anal rays; ventral adipose fin behind anus and ended well in front of anal fin; maximum height of ventral adipose fin ca. 1 / 6 of that of body; body color light, transparent when fresh; band of small melanophores on dorsum (100–200 µ in diameter); 23–24 clearly separated, black, peritoneal sections; lateral line extends over half of anal-fin base; lateral-line scales with two large pores; ratio of height to length of lateral-line scales 7: 9 ”.

Material examined.

• MCZ 39460 (3, 150–157), 21°50'50.8"N, 84°36'44.5"W, Cuba, Caribbean Sea , near surface, 26 Mar. 1939 . • USNM 407802 (158), R/V Miguel Oliver, 17°42'15.8"N, 87°52'49.8"W, Belize, Caribbean Sea , 31 Jan. 2011 . • USNM 438714 (159 mm SL), 15°33'17.6"N, 61°27'53.6"W, Windward Islands, Dominica, Caribbean Sea , 8 Mar. 2016, coll. L. A. Weigt & T. Christiaan .

Diagnosis.

A species of Stemonosudis distinguished by the combination of characters: a rather slender body, body depth 19–25 times in SL; DFO behind tip of pelvic fin and around middle of V – A, V – D 40.0–52.0 % V – A; anus above tip of appressed pelvic fin; lateral-line scales: PVLL 41–43, PDLL 51–55, PALL 81–84, TLL 85–97; vertebrae: PVV 41–42, PHV 45–46, PDV 52–53, PAV 65–66, CV 58–60, TV 103–105; and body dark dorsally and pale ventrally without blotches.

Description

(based on 5 specimens examined herein). Body relatively slender as in most Stemonosudis species; strongly compressed. Caudal peduncle moderately long, its length about 1.1–1.5 times eye diameter. Ventral adipose fin weakly developed, with a narrow transparent membrane along ventral abdominal ridge in front of pelvic fin and well-developed along ventral margin between anus and anal fin. Anus located approximately above tip of the appressed pelvic fin, about midpoint of V – D.

Head relatively long, its length 4.7–5.0 in SL; snout long and pointed, 1.8–1.9 in HL and 8.4–8.9 in SL. Mouth terminal, moderately large, its gape extending to slightly more than one eye diameter before eye with mouth opened; tip of lower jaw slightly upturned, with a small fleshy knob. Eye moderately small. Interorbital space rather narrow, 12.4–13.7 in HL; some straight symmetric ridges on top of head and snout. Posterior end of maxilla extending to about 1 / 2 eye diameter before the eye. A skin fold originating from about middle of snout and ending near a vertical through anterior margin of eye pupil. Two nostrils at or slightly before a vertical through posterior end of maxilla, situated about 3 / 5 eye diameter in front of eye. Numerous sensory canals on snout, cheek, operculum, and jaws; numerous sensory pores on dorsal surface of snout; irregular rows of small pores on under surface of lower jaw.

Filaments present on all four gill arches. Fourth arch connected almost entirely to the gill cavity wall by membranes. Pseudobranchs present, anterior half inside a deep pocket.

Dorsal fin small with a short base. DFO well behind pelvic fin and middle of the fish, at about middle of V – A or slightly before, V – D 40.0–52.0 % V – A. Pectoral fin slender, upper rays distinctly longer than lower rays; its base slightly behind a vertical through posterior margin of gill cover, upper base tangent to a horizontal though lower margin of eye. A small fleshy pocket behind pectoral-fin base. Pelvic fin slightly behind middle of the fish; a small, slender axial scale behind pelvic fin base. Anal fin with a short base, originating about four-fifths along the fish. Adipose fin relatively large, its base about same as eye diameter, situated above rear portion of anal-fin base.

Two or 3 small fangs at tip of upper jaw, followed by single row of numerous (> 80) small retrorse teeth along upper jaw, becoming gradually smaller posteriorly. Vomerine teeth absent. Two or 3 depressible or fixed fangs at front of lower jaw, followed by two rows of fangs on lower jaw forming about 7 or 8 tooth pairs, those in inner row distinctly longer and depressible, with knife-like tips; those in outer row much shorter, fixed and retrorse. Two rows of fangs on each palatine, anterior teeth forming 5–9 widely-spaced tooth pairs, those in inner row depressible and distinctly longer than those of outer row, which are small and fixed; posterior portion with single row of 6–8 small fixed teeth. Two long rows of small retrorse teeth on tongue.

Gill rakers present on all gill arches, assumed not fully developed in specimens examined; small, shield-shaped, mostly with 1–3 small teeth and a narrow base, teeth not especially emergent over margin of gill arch. Teeth on pharyngeal arch slender, forming an oval patch with approximately 4 rows at middle. Single row of small teeth on each fifth ceratobranchial, both forming a V-shaped pattern.

Body scaleless, except for a single row of lateral-line scales originating above pectoral girdle and extending to about 2 / 3 of anal-fin base. Lateral-line scales relatively long, longer than high, becoming gradually smaller and narrower posteriorly; row of 2 (few with 3) pores on upper and lower margin of each scale, anterior pore larger; and pore on broader of each scale smaller. Luminescent duct absent.

Coloration. Body light gray, with unevenly distributed melanophores; large unpigmented areas on gill cover, abdominal region and body axis; dense melanophores on most surfaces of snout, both jaws and dorsal surface of head; dorsum densely covered with melanophores, these extending downward to lateral line; abdominal ridge with loosely arranged melanophores; lower half of body with scattered melanophores behind anus, these becoming gradually more dense posteriorly, forming a darker caudal peduncle; pectoral fin covered with few melanophores; other fins densely covered by melanophores. Gill chamber, gill arches and filaments unpigmented. Peritoneal sections 23–26.

Remarks.

Table 1 provides the morphometric data for our specimens compared to the two largest types (159.5 mm SL holotype and 105.5 mm SL paratype) mentioned in the original description. The morphometric and meristic values are generally consistent between these types and our specimens, with some exceptions as noted below. Our specimens have nostrils slightly anterior to the posterior end of the maxilla, whereas the holotype has nostrils positioned directly above the end of the maxilla (as observed in the original drawing; Post 1970). The snout length is shorter in the two types (8.7 % and 7.9 % SL, respectively) compared to our specimens (11.2–11.9 % SL). The eye diameter is slightly larger in our specimens (3.1–3.5 % SL), while the eyes are smaller in the two types (2.9 % and 2.3 % SL, respectively). Additionally, our specimens exhibit a greater number of total lateral-line scales (89–97) compared to the two types (86–87), which is within the variation range of Stemonosudis species.

In the Atlantic Ocean, only four Stemonosudis species were recorded. Stemonosudis siliquiventer differs from S. bullisi Rofen, 1962 in having origins of dorsal and pelvic fins well behind middle of space between pectoral-fin base to anal-fin base (vs. at about middle of the space); from S. intermedia in having 103–105 total vertebrae (vs. 111–121); and from S. gracilis ( Ege, 1933) in lacking blotches on dorsum and ventral margin (vs. 3 or 4 blotches on dorsum and 2 or 3 on ventral margin) and 23–26 peritoneal sections (vs. 14–15).

Moreover, in the Indo-Pacific region, S. siliquiventer is different from S. elegans ( Ege, 1933) (Indo-west Pacific) and S. miscella ( Ege, 1933) (western Pacific), S. multifasciata Ho, Russell, Graham & Psomadakis, 2019 (Indo-west Pacific), S. rothschildi Richards, 1967 (circumglobal), S. retrodorsalis Ho, Russell, Graham & Psomadakis, 2019 (Indo-west Pacific) and S. similis ( Ege, 1957) (western Pacific) in lacking blotches on dorsum and ventral margin (vs. several distinct blotches on dorsum and ventral surface) and 23–26 peritoneal sections (vs. 3–11); from S. molesta ( Marshall, 1955) ( New Zealand) in having 10 dorsal-fin rays (vs. 13) and 36–38 anal-fin rays (vs. 30); from S. distans ( Ege, 1957) (western Pacific) in having 36–38 anal-fin rays (vs. 34) and 23–26 peritoneal sections (vs. 17); from S. macurus ( Ege, 1933) (Indo-Pacific) in lacking distinct rows of large melanophores on dorsum (vs. two distinct rows of large melanophores on dorsum); and from S. elongata ( Ege, 1933) by having 36–38 anal-fin rays (vs. 48–51).

Figures

Figure 2. Stemonosudis siliquiventer Post, 1970, USNM 438714, 159 mm SL A lateral view B lateral view of trunk, arrow points to the anus and bars indicate origins of pelvic fin (VFO), dorsal fin (DFO) and anal fin (AFO).

Figure 3. Distribution map of Stemonosudis siliquiventer Post, 1970 in the western central Atlantic. Star: holotype, circles: from Post (1970), and triangles: this study.