Eustomias (Haploclonus) stamen, 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 : 98

Eustomias (Haploclonus) stamen sp. nov.

Figure 2 ; Tables 1–2

Holotype. NMMB-P 12724, 102.8 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.

Diagnosis. A species of subgenus Haploclonus with a unique barbel structure: barbel short, its length 19.6% SL; terminal bulb rounded and large, its greatest width almost 5 times of stem width; a simple, thin appendage of branch arising near base of terminal bulb with its distal tip extending beyond terminal bulb; two long (longer than terminal bulb) and one short (as long as barbel diameter) filaments on distal tip of terminal bulb; branch and terminal filaments lacking pigments, luminous swellings, and secondary branches; stem unpigmented, axis pigmented. Meristic characters also unique in the subgenus: dorsal-fin rays 20; anal-fin rays 32; IP 8; PV 33; VAV 14.

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

Lower jaw slightly curved. Seven teeth on premaxilla, 1st and 2nd long and sharp, posterior 4 teeth depressible; 15 strongly oblique comb-like teeth on maxilla; 9 teeth on dentary, 3rd, 4th, 6th, 7th, and 9th teeth depressible. Postorbital photophore oblong and very small, its diameter shorter than anteriormost upper jaw tooth.

Etymology. The specific name of the new species, stamen , in reference to the diagnostic character of the species which a simple, thin appendage of branch arising near base of terminal bulb which looks like a stamen of flower.

Distribution. Eustomias stamen 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.

Remarks. The present specimen was identified as a species of the subgenus Haploclonus by the following combination of characters: a simple tapering branch, ending a little before the terminal bulb of the barbel; external pigmentation of the barbel absent; pectoral-fin rays 3; pelvic-fin rays 7; number of teeth on jaws few, 2nd tooth on upper jaw very sharp ( Regan & Trewavas 1930; Prokofiev 2018; only typical characters listed). Although Prokofiev (2018) indicated that length of the barbel ranged 25–89% SL for subgenus Haploclonus , the present species has a distinctly short barbel (19.6% SL). Regan & Trewavas (1930) recognized 5 species in the subgenus Haploclonus and Prokofiev (2018) described a new species from the southeastern Pacific Ocean.

Of the species previously recognized in the subgenus Haploclonus , the present new species differs in having a unique structure of the barbel (see Diagnosis). Eustomias stamen is most similar to Eustomias (Haploclonus) enbarbatus Welsh 1923 , which was described on the basis of holotype and a paratype collected from the northwestern Atlantic Ocean. Eustomias (Haploclonus) brevifilis Regan & Trewavas (1930) described from northern Atlantic Ocean known as a junior synonym of E. enbarbatus , thus the ranges of comparative meristic data of both species are combined below. Eustomias stamen sp. nov. differ from E. enbarbatus in having a large bulb, its greatest width almost 5 times of stem width (vs. small, its greatest width less than twice of stem in E. enbarbatus ), three unbranched terminal filaments on barbel (vs. four or five filaments, the longest branched), 32 anal-fin rays (vs. 34–36), IP 8 (vs. 7), PV 33 (vs. 26–27), VAV 14 (vs. 11–12) [ Regan & Trewavas (1930)].

Figures

FIGURE 2. Eustomias (Haploclonus) stamen sp. nov. from Taiwan, NMMB-P12724, holotype, 102.8 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.