Eustomias (Nominostomias) tritentaculatus, Koeda & Ho, 2019

Koeda, Keita & Ho, Hsuan-Ching, 2019, Review of the genus Eustomias (Stomiiformes: Stomiidae: Melanostomiinae) of Taiwan, with descriptions of three new species, Zootaxa 4702 (1), pp. 94-106 : 101

Eustomias (Nominostomias) tritentaculatus sp. nov.

Figure 4 ; Tables 1–2

Holotype. NMMB-P 30396, 130.9 mm SL, off Dong-gang (ca. 22°39ʹN, 120°24ʹE), Pingtung , South China Sea, Tai- wan, 16 Mar. 2005, obtained at fish-landing ground at Dong-gang, collected by commercial mid-water trawling.

Paratype. NMMB-P 22760, 120.4 mm SL, same as holotype, 3 Nov. 2011 .

Diagnosis. A species of subgenus Nominostomias with a unique barbel structure: barbel moderately long, its length 65.3% SL; terminal bulb small, its length 1.2% SL; three terminal filaments, one of which thicker than others with few pigmentations near base, all filaments simple and lacking bulblets and secondary branches; longest filament length 4.1% SL; axis of stem weakly pigmented; a distinct ring-shaped black spot surrounding base of bulb. Some of the meristic characters are also distinct: anal-fin rays 35; IP 7; PV 34; VAV 19; OV 31; VAL 19.

Description. Counts and measurements are given in Tables 1 and 2.

Jaws not curved. Twelve teeth on premaxilla, anterior 2 teeth (and 6th in paratype) fixed; 8–10 strongly oblique comb-like teeth on maxilla; 15–18 teeth on dentary, all teeth (except for 2nd in holotype) movable. Postorbital photophore rounded and small, its diameter as long as anteriormost upper jaw tooth.

Etymology. The specific name of the new species, tritentaculatus , in reference to the three terminal filaments, which is diagnostic of the species.

Distribution. Eustomias tritentaculatus sp. nov. is currently only known from southwestern Taiwan. The holotype was collected in the upper 100 m by a mid-water trawl targeting Sakura-shrimp ( Lucensosergia lucens ).

Remarks. The present specimens were identified as a species of the subgenus Nominostomias by the following combination of characters: a single terminal bulb on barbel; three terminal filaments of the bulb; no tapering branch on the barbel; external pigmentation of the barbel absent (axis pigmented); pectoral-fin rays 3; pelvic-fin rays 7; vertebrae 66–68; number of teeth on jaws high ( Regan & Trewavas 1930; Gibbs et al. 1983; Prokofiev 2018; only typical characters listed). Gibbs et al. (1983) reviewed this subgenus and recognized 38 valid species, 25 of which were described as new. They also separated this subgenus into five species groups on the basis of the structure of the barbels. Eustomias tritentaculatus sp. nov. has a structure of barbel with the species of their group IV (8 species), species of which have a single terminal bulb with one to three terminal filaments. Eustomias tritentaculatus sp. nov. is most similar to Eustomias (Nominostomias) cancriensis Gibbs, Clarke & Gomon, 1983 from the western and central-north Pacific oceans, but differs in having a longer barbel, its length 65.3% (vs. 47–53% SL in E. cancriensis ), a distinct ring-shaped black spot at base of bulb (vs. no pigmentation at base of bulb), and fewer anal-fin rays counts 35 (vs. 39) ( Gibbs et al. 1983). Eustomias tritentaculatus sp. nov. is also similar to Eustomias (Nominostomias) gibbsi Johnson & Rosenblatt, 1971 from the Pacific Ocean; both have a black spot at the base of the bulb. However, Eustomias tritentaculatus sp. nov. differs from the latter in having three terminal filaments (vs. single in E. gibbsi ), barbel length 65.3% (vs. 30–52% SL), and a longer terminal filament, its maximum length 4.1% SL (vs. 1.6–2.0 in the similar sized specimens) ( Gibbs et al. 1983).

Figures

FIGURE 4. Eustomias (Nominostomias) tritentaculatus sp. nov. from Taiwan, NMMB-P30396, holotype, 130.9 mm SL. Top: preserved specimen; middle: closeup illustration of distal part of barbel; bottom: diagram of dentition. Black and white color of teeth indicate fixed and movable, respectively.