Eustomias (Dinematochirus) dendrobium, 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 : 95-98

Eustomias (Dinematochirus) dendrobium sp. nov.

Figure 1 ; Tables 1–2

Holotype. NMMB-P 30621, 117.8 mm SL, off Dong-gang (ca. 22°39ʹN, 120°24ʹE), Pingtung , South China Sea, Tai- wan, 10 Sept. 2018, obtained at fish-landing ground at Dong-gang, collected by commercial mid-water trawling.

Diagnosis. A species of subgenus Dinematochirus with a unique barbel structure: barbel short, its length 13.9% SL; three branches arising at distal one-fourth of the barbel stem; distal tip of three branches extend distinctly beyond terminal bulb; medial branch thicker than lateral branches; two long and one very short secondary branches arising from middle of medial branch; two short secondary branches arising from near base of each lateral branch; each branch with 5–14 dendritic appendages comprised 1–15 tiny luminous swellings; terminal bulb simple, lacking terminal filaments; stem and branches solidly pigmented (skin rubbed off in some parts) except for dorsolateral surface of terminal bulb and blotchy unpigmented distal 1/3 of secondary branches of medial branch.

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

Jaws not curved; 7 teeth on premaxilla, 2nd, 4th, and 5th depressible; 8 strongly oblique comb-like teeth on maxilla; 7 teeth on dentary, all depressible, except for 3rd. Postorbital photophore large, its diameter as same as pupil diameter; dorsal third of postorbital photophore covered by black skin.

Etymology. The specific name of the new species, dendrobium , in reference to the diagnostic character of the species, which resembles the flowers of an orchid: branches of barbel with many dendritic appendages of tiny luminous swellings.

Distribution. Eustomias dendrobium sp. nov. is currently only known from southwestern Taiwan. The holotype was collected from shallower than 100 m, by a mid-water trawl targeting Sakura-shrimp ( Lucensosergia lucens ).

Remarks. The species of the genus Eustomias are difficult to identify because most of the species were described based only on structure of the barbel. The present specimen was identified as a species of the subgenus Dinematochirus by the following combination of characters: 3 branches on stem of the barbel; the barbel is uniformly black; photophores of the barbel stem absent; length of the barbel 13.9% SL; pectoral-fin rays 2; pelvic-fin rays 7; number of depressible teeth more than fixed teeth on jaws ( Regan & Trewavas 1930; Prokofiev 2018; only typical characters listed).

Although Prokofiev (2018) indicated that terminal filaments of the bulb present in members of the subgenus Dinematochirus , are actually absent in Eustomias (Dinematochirus) bulbiramis Clarke 2001 and Eustomias (Dinematochirus) triramis Regan & Trewavas 1930 ; they are also absent in our new species. This suggest that a presence of terminal filaments is not diagnostic for the subgenus. Gibbs et al. (1983) re-defined the Dinematochirus and recognized 12 valid species, of which, 10 were described from the Atlantic. Clarke (1998; 1999; 2000; 2001) subsequently described 26 new species and concluded that some of the species occur in both the Atlantic and the Indo-Pacific.

Of the species previously recognized in the subgenus Dinematochirus , the present new species differs in having a distinctly unique structure of the barbel (see Diagnosis). Eustomias dendrobium sp. nov. is most similar to E. bulbiramis and E. triramis in always and usually lacking a terminal filament on the terminal bulb on the barbel, respectively. However, E. dendrobium differs from them in having the structure of median branch with long secondary branches from the lateral branches (vs. similar), distal tip of branches extending distinctly beyond terminal bulb (vs. reached or distinctly shorter), and almost solidly pigmented branches (vs. unpigmented) ( Regan & Trewavas 1930; Clarke 2001). In addition, E. bulbiramis has prominent bulblets at about middle of branches, and E. triramis has a large subovate terminal bulb, whereas E. dendrobium sp. nov. lacks both.

Figures

FIGURE 1. Eustomias (Dinematochirus) dendrobium sp. nov. from Taiwan, NMMB-P30621, holotype, 117.8 mm SL. Top: fresh condition 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 1. Meristic 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	ASIZP64170	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
Counts
Dorsal-fin rays	24	20	damaged	20	22	23	24	N/A
Anal-fin rays	43	32	35	33	36	35	29+	35
Pectoral-fin rays	2	3	3	3	3	3	3	3
Pelvic-fin rays	7	7	7	7	7	7	7	7
Vertebrae	63	N/A	57	58	N/A	66	68	68
Photophores
IP	damaged	8	7	7	8	8		7
PV	30	33		28	31	31	34	34
VAV	17	14	12	12	13	17	18	19
AC	20	20	22	21	18	19	damaged	damaged
OV	28	26	26	27	29	33	32	31
VAL	15	13	12	12	14	17	18	19
BR	damaged	11	11	11	10	11	10	damaged