Ophichthus megalops Asano, 1987

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 : 141-143

Ophichthus megalops Asano, 1987

(English name: Large Eye Snake Eel)

(Taiwanese common name: ƛēķḋ)

Ophichthus megalops Asano, 1987:135 (type locality: Kumano-nada, off Owase, Mie Prefecture, Japan); Hatooka 2000:223 (off Owase, Mie); Hatooka 2013:223 (off Owase, Mie); McCosker 2010:28 (off Owase, Mie, Japan); McCosker et al. 2012:7 ( Japan, key only); McCosker & Ho 2015:72 ( Taiwan, key only); Ho et al. 2015:173 (in part; Nan-fang-ao, Taiwan).

Specimens examined. FAK 19057, holotype, 325 mm TL, sexuality unknown, Kumano-nada coast, off Owase, Mie Prefecture, Japan, 360 m depth, bottom trawl, collected by H. Asano ; KAUM–I. 125145, 330 mm TL, sexuality unknown, Dong-gang , Taiwan, depth unknown, bottom trawl, 26 Dec. 2018, collected by K. Koeda ; NMMB-P12006 , 7 specimens, 288–500 mm TL, sexuality unknown, Nan-fang-ao, Taiwan, depth unknown, bottom trawl, 11 Mar. 2011, collected by H.-C. Ho ; NMMB-P 12193, 408 mm TL, sexuality unknown, Nan-fang-ao, Taiwan, 300–400 m depth, bottom trawl, 12 Jan. 2011, collected by H.-C. Ho ; TOU-AE 6871–6878, 8 specimens, 299–442 mm TL, 7 mature females and 1 immature male, Nan-fang-ao, Taiwan, 300–400 m depth, bottom trawl, 15 Apr. 2013, collected by Y.-C. Chiu ; TOU-AE 7153, 375 mm TL, sexuality unknown, Nan-fang-ao, Taiwan, 300–400 m depth, bottom trawl, 24 Jun. 2013, collected by Y.-C. Chiu.

Diagnosis. A species of Ophichthus with a dark-tipped anal fin, and the following combination of characters: head 10.1–11.5% TL; tail 54.5–57.4% TL; snout blunt, 19.6–22.9% HL; eye large, 92.4–110.6% of snout length and 14.0–22.8% HL; dorsal-fin origin well behind pectoral-fin tip by about three times pectoral-fin length; pectoral fin short, pedal-shaped, tip not filamentous; anterior-nostril tube whitish; posterior nostril a hole above upper lip with a tiny flap anteriorly; teeth on maxilla biserial; SO 1+4; POM 6+3; total vertebrae 162–168 and MVF 31-61-164.

Description. Counts and measurements are shown in Table 1 . Body long, subcylindrical, its depth at gill openings 22.2–30.3 in TL; tail slightly compressed posteriorly, its depth reduced gradually, tip elongate ( Fig. 1A ).

Head relatively large, branchial basket moderately expanded; head 8.7– 9.9 in TL; head and trunk 2.2–2.3 in TL; snout short, weakly acute, its length generally slightly longer than 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, 2.1–2.2 in upper jaw and 4.4–7.1 in head; anterior nostril a simple tube with a shallow notch on rim anteriorly; posterior nostril a hole opening outside mouth, above upper lip, slit-like with a short slim 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. 2A ).

Dorsal and anal fins relatively low, ending with a ridge almost equal to half of snout length; dorsal-fin origin behind pectoral-fin tip, 2.5–4.3 times pectoral-fin length (2.5 in holotype), behind level of gill opening and 1.2–1.5 times in HL (1.2 in holotype); caudal fin absent; pectoral fin short, pedal-shaped, its tip pointed but not filamentous.

Head pores small but obvious; arrangement of sensory pores on head as follows ( Fig. 2A ): one + four on supraorbital, one pore above the posterior rim of posterior nostril; three + three on infraorbital, one between anterior and posterior nostrils; six on mandible and three on preopercle; midtemporal and interorbital pores present. Lateral-line pores almost complete, 8–10 (10 in holotype) in branchial basket, 28–35 (32) anterior to dorsal-fin origin, 59–64 (61) anterior to anus, and 137–146 (141) in total, canal and pores absent in 0.6–0.9 times (0.7) of HL.

Teeth relatively small, conical, pointed, weakly recurved posteriorly; teeth on maxilla biserial, those on outer row smaller and arranged close-set; mandibular teeth arrangement X-shaped: biserial on site near snout (less, 2–3) and rictus site (more, ca. 20), others uniserial ( Fig. 2B, C ); vomerine teeth biserial anteriorly and uniserial posteriorly; intermaxillary teeth arranged in a broken circular pattern, fused with row on vomer.

Coloration when fresh ( Fig. 1 ): head and body bluish to deep brownish dorsally and whitish on belly; peritoneum silver gray, with numerous minute, black dots along myomeres ( Fig. 1B ); anus generally without surrounding, darker marking or rarely less faded melanophores (only KAUM–I. 125145); tube of anterior nostril whitish; sensory pores not marginated. Dorsal fin white without darker margin; anal fin pale except distinct black end about 1/2 HL from tail tip ( Fig. 1C ); pectoral fin white. After preservation in 10% formalin and transferring in 75% ethanol, body coloration becomes monotonous.

Etymology. The scientific name megalops refers to the remarkably large eye ( Asano 1987).

Distribution. Known from off Owase, Mie Prefecture, Japan (type locality); Nan-fang-ao, and Dong-gang, Taiwan, 300–400 m depth ( Asano 1987; this study).

Figures

FIGURE 1. A, Fresh specimen of Ophichthus megalops, TOU-AE6872, 442 mm TL, Nan-fang-ao, Yi-Lan, Taiwan; B, peritoneum of O. megalops, TOU-AE6875, 349 mm TL, Nan-fang-ao, Taiwan; C, black-tipped anal fin of O. megalops, TOU- AE6872. Arrow indicates origin of dorsal fin.

FIGURE 2. A, Lateral view of head of Ophichthus megalops, TOU-AE6872, 442 mm TL, Nan-fang-ao, Yi-Lan, Taiwan; B, arrangement of teeth on maxilla, palatal area; and C, mandible of Ophichthus megalops, TOU-AE6873, 367 mm TL, Nan-fangao, Yi-Lan, Taiwan. Arrows indicate interorbital (left) and mid-temporal (right) pores.

Tables

TABLE 1. Measurements (%) and counts of Ophichthus megalops, O. semilunatus sp. nov. and O. brevidorsalis sp. nov.

	Ophichthus megalops			O. semilunatus sp. nov.	O. brevidorsalis sp. nov.
	Holotype	Non-type specimens (n=18)		Holotype	Holotype
TL (mm)	326	288–500		500	398
		Mean	Range
HL/TL	11.0	10.6	10.1–11.5	9.4	9.5
Preanal length/TL	44.2	44.2	42.6–45.5	42.4	40.2
Tail length/TL	55.5	55.8	54.5–57.4	57.5	59.8
Predorsal length/TL	24.6	24.8	22.4–28.5	20.7	30.4
Body depth at gill opening/ TL	4.0	3.8	3.3–4.5	3.3	4.3
Body width at gill opening/ TL	3.9	3.0	2.6–3.6	2.7	3.4
Body depth at mid-anus/TL	3.7	3.2	2.7–3.8	2.6	2.5
Body width at mid-anus/TL	3.7	2.9	2.7–3.2	2.7	2.7
Snout length/HL	21.1	21.2	19.6–22.9	13.0	14.0
Eye diameter/HL	20.3	20.4	14.0–22.8	21.4	27.7
Mouth gape length/HL	46.8	46.7	42.9–49.8	42.1	45.1
Lower-jaw length/HL	41.0	44.4	39.6–48.2	-	41.6
Gill opening length/HL	9.0	18.7	11.7–24.9	19.0	19.4
Interorbital width/HL Pectoral-fin length/HL Counts	18.1 30.7	18.7 33.6	16.7–21.3 30.0–38.0	17.7 30.8	16.9 35.2
SO	1+4	1+4	-	1+3	1+3
IO	3+3	3+3	-	3+3	3+3
POM	6+3	6+3	-	6 or 7+2	6+2
ST	3	3	-	3	3
Lateral-line pores before gill opening	10	9	8–10	8	7
Lateral-line pores before dorsal-fin origin	32	32	28–35	30	48
Lateral-line pores before anus	61	62.1	59–64	65	65
Total lateral-line pores	141	142.4	137–146	158	148
Predorsal vertebrae	29	30.6	28–35	29	43
Preanal vertebrae	60	60.8	59–63	64	61
Total vertebrae	160	164.3	162–168	176	164