Eustomias (Nominostomias) perplexus Gibbs, Clarke & Gomon 1983

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 : 102-105

Eustomias (Nominostomias) perplexus Gibbs, Clarke & Gomon 1983

Figure 5 ; Tables 1–2

Material examined. NMMB-P 12063, 123.1 mm SL, off Dong-gang (ca. 22°39ʹN, 120°24ʹE), Pingtung , South China Sea, Taiwan, 28 Jan. 2011, obtained at fish-landing ground at Dong-gang, collected by commercial mid-water trawling .

Diagnosis. A species of subgenus Nominostomias with a unique barbel structure: barbel moderately long, its length 72.6% SL; terminal bulb small, its length 0.9% SL, longitudinal length greater than width; a single terminal projection with two horn-shapes, its maximum length 0.3% SL; axis of stem weakly pigmented. Some of the meristic characters are also distinguishable: dorsal-fin rays 23–24; anal-fin rays 35; IP 8; PV 31–34; VAV 17–18; OV 32–33; VAL 17–18.

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

Jaws not curved. Eleven teeth on premaxilla, 1st to 3rd, 5th, 7th–9th fixed; 10 strongly oblique comb-like teeth on maxilla; 15 teeth on dentary, 1st, 2nd, 5th, 7th, and 9th fixed. Postorbital photophore oblong and small, its diameter as long as anteriormost upper jaw tooth.

Distribution. Eustomias perplexus sp. nov. is widely known from western, central equatorial, and northeastern Pacific Ocean.

Remarks. The present specimen is presumed to be a species of the subgenus Nominostomias in having the following combination of characters: a single terminal bulb on barbel; a single terminal projection on 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 68; number of teeth on jaws high ( Regan & Trewavas 1930; Gibbs et al. 1983; Prokofiev 2018; only typical characters listed). Eustomias perplexus has a structure of barbel consistent with the species of group V (5 species comprised) of Gibbs et al. (1983), which share a single terminal bulb with either a dome-like or finger-like projection at its distal end. Eustomias perplexus is most similar to Eustomias (Nominostomias) longibarba Parr, 1927 of the Atlantic Ocean. However, Gibbs et al. (1983) provided no diagnostic characters, except that the former has a shorter terminal projection on bulb than the latter. Although they indicated the distributional difference between these two species in their “Key to species”, some of the species of genus Eustomias were known to have circumglobal distribution in the warm waters. We tentatively identified the Taiwanese specimen as E. perplexus on the basis of its very short terminal projection on bulb and the distribution; however, its validity needs further investigation.

Figures

FIGURE 5. Eustomias (Nominostomias) perplexus from Taiwan, NMMB-P12063, 123.1 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.

Tables

TABLE 2. Morphometric data of the specimens of genus Eustomias from Taiwan.

Subgenus	Dinematochirus		Haploclonus				Nominostomias
Species	E. dendrobium	E. stamen		Eustomias sp.		E. tritentaculatus		E. perplexus
Specimen	NMMB-P30621	NMMB-P12724	NMMB-P28088	NMMB-P22420	ASIZP 64170	NMMB-P22760	NMMB-P30396	NMMB-P12063
Standard length (SL)	117.8	102.8	100.7	126.6	48.6	120.4	130.9	123.1
Measurements (%SL)
Body depth	8.3	6.3	7.9	7.3	6.0	6.6	5.1	6.7
Head length (HL)	13.2	13.6	12.2	10.4	14.4	14.1	13.4	13.2
Snout to vent	69.7	69.5	75.3	73.4	70.2	70.2	damaged	68.2
Pectoral-fin base to vent	50.5	49.1	56.6	56.3	54.1	52.9	damaged	46.5
Vent to caudal-fin base	29.5	30.1	29.6	25.9	31.5	27.8	damaged	28.3
Pre-dorsal-fin length	85.1	86.6	86.9	83.1	83.7	79.2	84.2	83.3
Pre-anal-fin length	71.7	74.2	75.3	74.6	71.6	70.4	76.8	67.7
Pre-pelvic-fin length	56.2	58.1	59.6	59.3	57.2	56.8	60.5	55.6
Barbel length	13.9	19.6	31.1+	24.4+	25.9+	41.1+	65.3	72.6
Measurements (%HL)
Snout length	40.6	46.4	29.3	36.4	42.9	38.8	49.7	47.5
Eye diameter	26.3	22.9	27.6	25.8	27.1	20.6	16.0	21.0
Body interorbital width	21.1	13.6	17.1	15.9	15.7	12.4	9.7	11.1
Barbel length	107.5	168.6	254.5+	234.5+	180+	291.1	449.0	539.4