Eustomias (Haploclonus)

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 : 99-100

Eustomias (Haploclonus) sp.

Figure 3 ; Tables 1–2

Eustomias bifilis not Gibbs 1960: Shen & Wu 2011, 196, unnumbered illustration; Shao (2019). Materials examined. NMMB-P 28088, 100.7 mm SL, off Dong-gang (ca. 22°39ʹN, 120°24ʹE), Pingtung, South China Sea, Taiwan, 22 Jan. 2018, obtained at fish-landing ground at Dong-gang , collected by commercial mid-water trawling; NMMB-P 22420, 126.6 mm SL, same as former, 29 Mar. 2015 ; ASIZP 64170 , 48.6 mm SL, off southwestern Taiwan (ca. 22°04ʹN, 120°27ʹE), South China Sea, Taiwan, collected by mid-water trawling, 529–530 m depth, 28 May 2003 .

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

Jaws not curved (NMMB-P28088) or lower jaw slightly curved (NMMB-P22420 and ASIZP 64170). NMMB- P28088: 8 teeth on premaxilla, 1st and 2nd long and sharp, 5th, 6th, and 8th teeth movable; 7 strongly oblique comb-like teeth on maxilla; 9 teeth on dentary, 3rd, 5th, 6th, 8th, and 9th teeth movable. NMMB-P22420: 6 teeth on premaxilla, 2nd long and sharp, 2nd, 4th, and 6th teeth movable; 8 strongly oblique comb-like teeth on maxilla; 6 teeth on dentary, 2nd, 4th, and 6th teeth movable. ASIZP 64170: premaxilla damaged; 4 teeth remaining on dentary, 1st fixed. Barbel on lower jaw damaged on halfway, its remaining length 24.4–31.1% SL. Postorbital photophore oblong or rounded, and very small, its diameter shorter than anteriormost upper jaw tooth.

Remarks. Although the present two adult specimens (NMMB-P28088 and NMMB-P22420) have lost the terminal structure of the barbel, which is the most important character to identify the species, it is presumably a species of the subgenus Haploclonus because it has the following combination of characters: photophores of the barbel stem present on axis; 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). The juvenile specimen (ASIZP 64170) has lost not only the terminal structure of the barbel but also the premaxilla. However, the counts of body photophores and few teeth counts indicate it should be a species of this subgenus. For example, the specimen has 13 VAV, whereas in the most similar subgenus, Nominostomias , the least count known is 15 (mostly more than 16 or 17) ( Gibbs et al. 1983). Although it is not possible to identify the specimens to species they distinctly differ from E. stamen sp. nov. in having 33–36 anal-fin rays (vs. 32 in E. stamen ), PV 28–31 (vs. 33), VAV 12–13 (vs. 14), and a longer barbel, its length at least 24.4–31.1% SL (vs. 19.6% SL without damage).Although the two adult unidentified specimens have no remarkable difference in meristic and morphometric characters, the dentition of the specimens differs substantially ( Fig. 3 ). This suggests that these two adult specimens are different species. The present juvenile was the only specimen previously known from Taiwanese waters. Shen & Wu (2011) identified this specimen as Eustomias bifilis Gibbs 1960 , which is a very characteristic species has a single long branch from the main stem of the barbel. This identification was followed by Shao (2019). However, the barbel of the specimen was lost and it is not possible to determine the species.

Figures

FIGURE 3. Eustomias (Haploclonus) sp. from Taiwan. Top: fresh condition specimen, NMMB-P28088, 100.7 mm SL; middle: preserved specimen, NMMB-P22420, 126.6 mm SL; right bottom: diagram of dentition, NMMB-P28088; left bottom: diagram of dentition, NMMB-P22420. Black and white color of teeth indicate fixed and movable, respectively.