Stemonosudis adenensis Ho, 2025

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 adenensis Ho sp. nov.

Fig. 1 A – C , Tables 1 , 2 , 3 Common name: Brown Slender Barracudina

Holotype.

• USNM 306145 (186 mm SL), R/V BEINTA, cr. 14, haul 13, 11°15'35"N, 48°05'47"E, off Somalia, Gulf of Aden , Western Indian Ocean, 375 m, 15 Sep. 1986, coll. J. June .

Diagnosis.

A species of Stemonosudis with the following combination of characters: body brown with dorsum slightly darker, without black patches; nostrils slightly before vertical through posterior end of maxilla; anus above tip of appressed pelvic fin; lateral-line scales: PVLL 39, PDLL 48, PALL 59, TLL 81; vertebrae: PVV 38, PHV 42, PDV 46, PAV 59, CV 53, and TV 95; and total gill rakers 68.

Description.

Body slender and compressed, relatively short compared to most congeners. Caudal peduncle short, its length ca. 1.2 times eye diameter. Ventral adipose fin barely developed along abdominal ridge before pelvic fin, but well-developed along ventral margin between anus and AFO. Anus located above tip of appressed pelvic fin, well ahead of DFO by about base length of dorsal fin.

Head relatively long, its length 4.2 in SL; snout moderately long and pointed, its length 2.0 in HL or 8.2 in SL. Mouth terminal, moderately large, its gape extends to about one eye diameter before eye when mouth opened; tip of lower jaw slightly upturned, with small fleshy tissue at tip. Eye moderately large, its diameter 6.4 in HL. Interorbital space moderately broad, its width 13.6 in HL; some straight ridges on top of head and snout. Posterior end of maxilla extending to about 2 / 3 eye diameter in front of the eye, upper-jaw length 2.4 in HL. A skin fold originating from about middle of snout and ending near a vertical through anterior margin of eye. Two nostrils located slightly before a vertical through posterior end of maxilla, situated at about 2 / 3 eye diameter in front of eye, pre-nostril length 2.5 in HL. Numerous sensory canals on snout, cheek, operculum, and upper jaw; irregular rows of small pores on lower surface of lower jaw.

Gill filaments present on all four gill arches. Fourth arch mostly connected to inner surface of gill chamber by membranes. Pseudobranchs present, anterior half inside a deep pocket.

Dorsal fin small with short base, base length 6.9 in HL. DFO well behind pelvic fin and middle of the fish, well before middle of V – A, predorsal length 1.5 in SL. Pectoral-fin base slightly behind a vertical through posterior margin of gill cover, its upper base about same level of lower margin of eye, pectoral-fin length 2.9 in HL. A small pocket behind pectoral-fin base. Pelvic fin slightly behind middle of body, prepelvic length 1.8 in SL; a small, slender axial scale behind pelvic-fin base. Anal fin with a long base, originating on posterior fourth of body, base length 1.4 in HL. Adipose fin small, its base slightly smaller than eye diameter, situated above rear portion of anal-fin base.

Two small fangs at tip of upper jaw, followed by single row of numerous small retrorse teeth along upper jaw, gradually smaller posteriorly. Vomerine teeth absent. Two fangs at front of lower jaw, followed by 2 rows of fangs on lower jaw, forming about 7 tooth pairs, those in inner row distinctly long, depressible, with a knife-like tip; those in outer row much shorter, retrorse and fixed. Two rows of fangs on each palatine, anterior teeth forming 5 (right) or 7 (left) widely-spaced tooth pairs, those in inner row depressible and distinctly longer than those on outer row, small and fixed; posterior portion with single row of small fixed teeth. Two long rows of small retrorse teeth on tongue.

Gill rakers present on all gill arches; small, shield-shaped, usually with 3–5 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 about 4 (4–5) rows at middle. Single row of small teeth on fifth ceratobranchials, forming a V-shaped pattern.

Body scaleless, except for a single row of lateral-line scales originating above pectoral girdle and extending to a vertical through about 2 / 3 of length of anal-fin base. Lateral-line scales relatively long, longer than height, gradually smaller and becoming narrower posteriorly; single row of 3 large pores on upper and lower margin of each scale, middle pore smaller. Luminescent duct absent.

Coloration. When preserved, body brown with dorsum darker. Dense melanophores covering dorsal half of body above lateral line; loosely arranged melanophores surrounding the lateral-line scales, leaving a row of indistinct pale dots along lateral line, and extending to lower half of abdomen in front of pelvic fin, leaving a pale space below; a broad, dense band of melanophores along ventral margin of abdomen; loosely arranged melanophores on lower half of body behind VFO, gradually denser in arrangement posteriorly. Head, snout and isthmus unevenly covered with melanophores, leaving a pale space on gill cover. Pectoral fin pale with upper rays covered with scattered melanophores. Pelvic-fin rays lightly covered with melanophores. Dorsal, anal and caudal fins densely covered with melanophores. Mouth cavity and gill chamber pale, without melanophores. Abdominal cavity with black peritoneal membrane, except for lower 1 / 3 of the cavity, which is uniformly pale and lacking melanophores. Fresh coloration unknown but assumed similar to that of preserved condition.

Size. The holotype, 186 mm SL, is a female with small ovaries and small eggs. It may be near mature size, which would indicate this may be a small species compared with congeners.

Etymology.

Named for the type locality, Gulf of Aden in the Western Indian Ocean.

Comparisons.

Stemonosudis adenensis sp. nov. can be distinguished by having 95 total vertebrae, which is fewer than most congeners (98–121, usually> 100; see Table 3 ). Among the species with <95 total vertebrae (Table 3 , lines 1–6), S. adenensis can be differentiated from the three species in the S. rothschildi complex, viz. S. multifasciata ; S. retrodorsalis ; and S. rothschildi , by its uniformly brown body, lacking blotches (vs. uneven pigmentation with distinct blotches on the dorsal and ventral margins) and a relatively anterior placement of the dorsal fin (PDV 46, vs. 49–58). For more detailed information on the species complex, see Ho et al. (2019 b).

Stemonosudis adenensis sp. nov. differs from S. bullisi Rofen, 1963 , in having a higher number of total vertebrae (95, vs. 84); placement of the pelvic fin closer to the dorsal fin than to the pectoral fin (prepelvic length 57.0 % SL), compared to the pelvic fin being at about the midpoint between the pectoral and anal fins (prepelvic length 48.1 % SL) in S. bullisi ; and the nostrils slightly before a vertical through posterior end of maxilla (vs. well before in S. bullisi ). It differs from S. macrura Ege, 1933 in having a uniformly brown dorsum (vs. two distinct rows of large melanophores on the dorsum in S. macrura ); a distinctly greater number of prehaemal vertebrae (42 vs. 29–33); and nostrils slightly before a vertical through posterior end of maxilla (vs. well before).

In addition, S. adenensis sp. nov. is also similar to Dolichosudis fuliginosa Post, 1969 , which has a uniformly black body. However, S. adenensis sp. nov. can be distinguished from D. fuliginosa by having fewer total vertebrae (95, vs. 100–104 in D. fuliginosa ), a relatively deep body (body depth 23.5 % HL, vs. 19–22 % HL), and nostrils positioned slightly before the posterior end of the maxilla (vs. nostrils above the end of the maxilla).

Remarks.

Although described from only a single specimen, collected 38 years ago, the holotype is in good condition, and its diagnostic characters are distinctive. Despite examining many specimens in collections from around the world and consulting the results of recent surveys in the Western Indian Ocean (S. Bogorodsky, pers. comm.), we found no other specimens exhibiting the same characteristics as S. adenensis . Because of the current hostilities in the Gulf of Aden, it is unlikely that any surveys will be conducted in the type locality in the near future; therefore, we do not hesitate to describe this specimen as new.

Figures

Figure 1. Stemonosudis adenensis sp. nov., USNM 306145, 186 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 trunk, arrow points to the anus and bars indicate origins of pelvic fin (VFO), dorsal fin (DFO) and anal fin (AFO).