Ophichthus semilunatus Hibino and Chiu, 2019

Hibino, Yusuke, Chiu, Yung-Chieh, Chen, Hong-Ming & Shao, Kwang-Tsao, 2019, Two new species of the genus Ophichthus from the western central Pacific Ocean with a redescription of Ophichthus megalops Asano, 1987 (Anguilliformes Ophichthidae), Zootaxa 4702 (1), pp. 140-154 : 144-147

Ophichthus semilunatus Hibino and Chiu sp. nov.

(New English name: Half-moon Blotch Snake Eel)

(New Taiwanese name: ÷ƞķḋ)

Ophichthus megalops (not Asano): Ho et al. 2015: 173 (in part; Da-xi).

Holotype. NMMB-P 17751, 500 mm TL, female with immature eggs, Da-xi , Yi-lan, northeastern Taiwan, depth unknown, bottom trawl, 12 Nov. 2012, collected by H.-C. Ho.

Diagnosis. A species of Ophichthus with a dark-tipped anal fin, and the following combination of characters: head 9.4% TL; tail 57.5% TL; snout not acute, 19.0% HL; eye large, 93.3% of snout length and 17.7% HL; dorsalfin origin well behind pectoral-fin tip by about three pectoral-fin lengths; teeth on maxilla triserial; anterior margin of anus with a half-moon shaped dark marking; SO 1+3; POM 6 or 7+2; predorsal vertebrae 29, preanal vertebrae 64, and total vertebrae 176.

Description. Counts and measurements (in mm) of the holotype: predorsal vertebrae 29; preanal vertebrae 64; total vertebrae 176; preanal lateral-line pores 65. Total length 500; head length 46.8; preanal length 212.0; tail length 287.5; predorsal length 103.5; body depth at gill opening 16.4; body depth at mid-anus 13.0; body width at gill opening 13.3; body width at mid-anus 13.5; snout length 8.9; eye diameter 8.3; upper-jaw length 19.7; gill opening length 4.3; interorbital width 6.1; isthmus width 10.0; pectoral-fin length 14.4; pectoral-fin base 4.5. Body long, subcylindrical, its depth at gill openings 30.5 in TL; tail slightly compressed posteriorly, its depth reduced gradually, its tip elongate ( Fig. 3 ).

Head relatively large, branchial basket moderately expanded; head 10.4 in TL; head and trunk 2.4 in TL; snout short, not acute, its length almost equal to eye diameter; no ventral groove on snout; lower jaw included in upper jaw, its tip slightly beyond anterior base of anterior-nostril tube; mouth large, rictus well behind a vertical from posterior margin of eye, with a short, additional fold below rictus; eye large, 2.4 in upper jaw and 5.6 in head; anterior nostril tubular, a simple tube with a shallow notch on rim anteriorly; posterior nostril a hole opening outside of mouth, above upper lip, the hole with an extremely tiny flap anteriorly; upper lip smooth, without protrusions, numerous small papillae on inner upper and lower lips; interorbital region smooth and mostly flat; gill opening constricted, located ventrolaterally ( Fig. 4A ).

Dorsal and anal fins relatively low, ending with a ridge equal to half of snout length; dorsal-fin origin behind pectoral-fin tip by 2.9 times pectoral-fin length, distance between level of gill opening to origin of dorsal fin 1.2 times in HL; caudal fin absent; pectoral fin short, its tip pointed, weakly filamentous.

Head pores small but obvious; arrangement of sensory pores on head as follows ( Fig. 4A ): one + three on supraorbital, no pore above the posterior rim of posterior nostril; three + three on infraorbital, one between anterior and posterior nostrils; six (seven right side) on mandible and two on preopercle; midtemporal and interorbital pores present. Lateral-line pores almost complete, 8 in branchial basket, 30 anterior to dorsal-fin origin, 65 anterior to anus, and 158 in total, canal and pores end about 0.9 HL before tail tip.

Teeth relatively small, conical, pointed, weakly recurved posteriorly; teeth on maxilla triserial, arranged irregularly in posterior part ( Fig. 4B, C ); mandibular teeth biserial, becoming irregularly triserial, inner teeth slightly larger than outer; vomerine teeth biserial anteriorly and uniserial posteriorly; intermaxillary teeth arranged in a circular pattern.

Coloration in preservative (50% isopropanol) of head and body bicolored, brown dorsolaterally and white ventrally, the border from rictus through insertion of pectoral fin, falling gradually toward end of anal fin; a dark halfmoon-shaped blotch along anterior margin of anus ( Fig. 5A ); tube of anterior nostril brownish but slightly paler than body; tip of lower jaw dusky; sensory pores not marginated. Dorsal fin extremely pale brown with melanophores but not marginated; anal fin pale white, except for a distinct black area around anal fin and base of the fin, its length about half of HL; pectoral fin white with a pale brown margin.

Distribution. Known only from the holotype collected from the northwestern Pacific Ocean, off northeastern Taiwan. Collecting depth unknown but estimated from deepwater.

Etymology. From the Latin, semi- (half) and lunatus (moon), relative to the half-moon blotch on the anterior margin of anus.

The table is based on Karreir (1983), Asano (1987), McCosker (1999, 2010), Tashiro et al. (2017) and present materials

Remarks. The new species has the characteristic coloration of a black tip on the anal fin. The character is shared only in seven known congeners. Table 1 shows the selected characters separating the black anal-fin tip species of Ophichthus . The shape of the snout is similar to O. kunaloa McCosker, 1979 and O. tomioi McCosker, 2010 but is easily discerned from the species by the position of dorsal-fin origin (well behind pectoral-fin tip in O. semilunatus sp. nov. vs. not behind in O. kunaloa and O. tomioi ). The position of the dorsal-fin origin of the new species is characteristic, having more predorsal vertebrae than other black anal-fin species except O. megalops and O. mystacinus (29 in O. semilunatus sp. nov. vs. 15–27 in O. aniptocheilos McCosker, 2010 , O. brachynotopterus Karrer, 1982 , O. exourus McCosker, 1999 , O. kunaloa , and O. tomioi ) ( Table 2 ), from O. mystacinus , having a shorter snout (19.0% HL vs. 22.7–28.0%), larger eyes (17.7% HL vs. 11.0–14.1%), one + three supraorbital pores (vs. one + four), and a shorter pectoral-fin (30.8% HL vs. 39.2–45.8%) ( McCosker 1999; 2010; Tashiro et al. 2017). The new species closely resembles O. megalops in the position of the dorsal-fin origin, counts of predorsal and preanal vertebrae, the shape of the posterior nostril, the shape of the pectoral fin and coloration of the anal fin with a black tip, resulting in the holotype of O. semilunatus sp. nov. having been misidentified as O. megalops . However, the new species can be distinguished from O. megalops by having more total vertebrae (176 vs. 157–168), three rows on the maxilla (vs. two rows, rarely one more row restricted to the posterior end), one + three supraorbital pores (vs. one + four), two preopercular pores (vs. three), the brownish tube of the anterior nostril (vs. mostly pale white), and the presence of a half-moon blotch on the anterior margin of the anus [vs. generally absent, or rarely, faded melanophores are present ( Fig. 5B )].

Figures

FIGURE 3. Preserved condition of Ophichthus semilunatus sp. nov., NMMB-P17751, holotype, 500 mm TL, Da-xi, Yi-lan, Taiwan. A, dorsal image; B, ventral image. Arrow indicates origin of dorsal fin.

FIGURE 4. A, lateral view of head of Ophichthus semilunatus sp. nov., NMMB-P17751, holotype, 500 mm TL, Da-xi, Yi-lan, Taiwan; B, arrangement of teeth on maxilla, palatal area; and C, mandible of Ophichthus semilunatus sp. nov. Arrows indicate interorbital (left) and mid-temporal (right) pores.

FIGURE 5. Enclosed view of anus. A, Ophichthus semilunatus sp. nov., NMMB-P17751, holotype, 500 mm TL, Da-xi, Yi-lan, Taiwan; B, O. megalops (irregular pattern), KAUM–I. 125145, 330 mm TL, Dong-gang, Taiwan.

Tables

TABLE 2. Information of the number of vertebrae, mandibular (M), preopercular pores (PO) and gill opening to dorsal-fin origin (GDO) for nine species of Ophichthus with dark-tipped anal fin.

Scientific name	Holotype	MVF	Range	M	PO	GDO/HL	Distribution
Ophichthus semilunatus sp. nov.	29/64/176	29-64-176	-	7	2	1.2	Taiwan
Ophichthus brevidorsalis sp. nov.	43/61/164	43-61-164	-	6 or 7	2	ca. 2.2	New Caledonia
Ophichthus aniptocheilos	16/59/140	16-59-140	-	6	2	0	Tonga
Ophichthus brachinotopterus	No information	25-60-172	167–178	6	2	ca. 1	Madagascar, New Caledonia, and Vanuatu
Ophichthus exourus	20/61/176	20-60-177	173–177	6 or 7	2	<1	New Caledonia
Ophichthus kunaloa	15/66/185	15-66-182	180–185	5	2	<1	Hawaii Island
Ophichthus megalops	29/60/160	31-61-164	157–168	6	3	1.2–1.5	Japan and Taiwan
Ophichthus mystacinus	35/62/174	34-61-170	162–177	6	2	ca. 1.2	New Caledonia
Ophichthus tomioi	16/62/169	16-62-169	166–189	6 or 7	2	<1	Philippines, Marquesas, Fiji, Seychelles