Ophichthus brevidorsalis Chiu & Hibino, 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 : 148-153

Ophichthus brevidorsalis Chiu & Hibino sp. nov.

(New English name: Short Dorsal-fin Snake Eel)

(New Taiwanese name: üṽñķḋ)

Holotype. ASIZP 61648, 398 mm TL, male with mature testis, New Caledonia, bottom trawl, 412–467 m depth, 30 Jan. 2002, collected by P.-F. Lee.

Diagnosis. A species of Ophichthus with a dark-tipped anal fin, and the following combination of characters: head 9.5% TL; tail 59.8% TL; snout pointed, 19.4% HL; eye large, 86.9% of snout length and 16.9% HL; dorsal-fin origin well behind pectoral-fin tip by more than five times pectoral-fin length; teeth on jaws biserial (single row posteriorly); anterior margin of anus without dark markings; SO 1+3; POM 6+2; predorsal vertebrae 43, preanal vertebrae 61, and total vertebrae 164.

Description. Counts and measurements (in mm) of the holotype: predorsal vertebrae 43; preanal vertebrae 61; total vertebrae 164; lateral-line pores before gill opening 7; predorsal lateral-line pores 48; preanal lateral-line pores 65; total lateral-line pores c.a. 148. Total length 398; head length 38; preanal length 160; tail length 238; predorsal length 121; body depth at gill opening 17.3; body depth at mid-anus 9.8; body width at gill opening 13.5; body width at mid-anus 10.7; snout length 7.4; eye diameter 6.4; upper-jaw length 17.1; gill opening length 8.1; interorbital width 5.3; isthmus width 10.5; pectoral-fin length 13.4; pectoral-fin base 4.2. Body moderately elongate, subcylindrical, its depth at gill openings 23.1 in TL; tail slightly compressed posteriorly ( Fig. 6 ).

Head relatively small, branchial basket expanded; head 10.5 in TL; head and trunk 2.5 in TL; snout short, not acute and its tip pointed, the length somewhat longer than eye diameter; lower jaw shorter than upper jaw, its tip slightly beyond anterior base of anterior nostril; mouth not large, rictus right behind a vertical from posterior margin of eye; eye located from the range within the last 1/3 of upper jaw; eye large, 2.7 in upper jaw and 5.9 in head; tubular anterior nostril with a shallow notch on rim anteriorly; posterior nostril a hole with a tiny flap anteriorly above upper lip; both of lips smooth, but many protrusions in mouth; gill opening located laterally ( Fig. 7A ).

Median fins low; tail become bare from the tip about half of snout length; dorsal-fin origin behind pectoral-fin tip by 5.3 times pectoral-fin length, distance between level of gill opening to origin of dorsal fin 2.2 times in HL; pectoral fin short with a filamentous end.

Head pores minute but visible; arrangement of cephalic pores as follows ( Fig. 7A ): one + three on supraorbital, no pore above the posterior rim of posterior nostril; three + three on infraorbital; six on mandible and two on preopercle; midtemporal and interorbital pores present. Lateral-line pores almost complete; 7 in branchial basket, 48 anterior to dorsal-fin origin, 65 anterior to anus, and c.a. 148 in total.

Teeth small, conical, pointed, slightly recurved posteriorly (especially on the snout tip region) and almost even size; teeth on maxilla biserial ( Fig. 7B, C ); mandibular teeth biserial; vomerine teeth biserial anteriorly, becoming one row posteriorly; intermaxillary teeth arranged in a circular pattern.

Coloration in preservative (75% ethanol): of body bicolored, brown dorsally and pale ventrally, the border from rictus and across through the base of pectoral fin, than falling gradually to the tail tip; anterior nostril pale; upper lip and tip of lower jaw dusky. Dorsal fin pale; anal fin whitish, its end presents a dark region, its length about a half of head; pectoral fin white without margin. The iris coloration has a dark background with numerous silver spots on it, which resembles stars in the sky.

Distribution. Known only from the holotype, from New Caledonia.

.

Etymology. From the Latin, brevidorsalis , meaning short dorsal fin, which refers to the diagnostic character of its dorsal-fin origin.

Remarks. The new species has the character of a posteriorly blackened of its anal fin. The position of the dorsal-fin origin of the new species is also characteristic, and can easily distinguish it from those species with their dorsal fin arising above or behind the pectoral fins, such as Ophichthus aniptocheilos , O. kunaloa , and O. tomioi . The new species is similar to O. megalops in the position of the dorsal-fin origin, and counts of preanal and total vertebrae, but the former can be separated from the latter by its number of preopercular pores (two vs. three in O. megalops ) and supraorbital pores (one + three vs. one + four), smaller eyes (2.7 vs. 2.1–2.2 in head), shorter head (9.5% of total length vs. 10.1–11.5%), longer tail (59.8% of total length vs. 54.5–57.4%), slightly shorter snout (19.4% of head vs. 19.6–22.9%), and having more predorsal vertebrae (43 vs. 28–35). The new species shares the same composition of supraorbital pores with O. semilunatus sp. nov. (one + three), as compared to other black-analfin species (one + four). The new species is also similar to O. brachynotopterus by the shape of its snout, condition of its posterior nostrils, and the position of its dorsal-fin origin, but differs in the shape of its pectoral fin (filamentous in O. brevidorsalis sp. nov. vs. not elongated in O. brachynotopterus ). The new species has the highest number of predorsal vertebrae among those dark anal-fin species (43 in O. brevidorsalis sp. nov.) ( Table 2 ).

In Table 1 , morphological ranges of O. brachynotopterus , O. megalops , O. mystacinus , and O. tomioi are expanded from their original descriptions. The vertebral counts overlap each other (except for O. aniptocheilos ), however, snout shape, pectoral-fin shape, and the condition of the posterior nostril can separate all similar species. A NJ tree constructed by partial COI gene sequences (552 bp after processed by BioEdit software) of five species with dark-tipped anal fins ( Table 3 ) that supported the separation of these species ( Fig. 8 ). Besides, in Table 4 , K2P distance matrix reveals that the distance lower than 0.01 among the same species, distance ranging from 0.105 to 0.160 among the 12 dark-tipped anal fin Ophichthus congeners, and the outgroup shows the distance ranging from 0.173 to 0.194. The COI sequences are currently not available for the two new species described herein. McCosker et al. (2012) speculated that the blackened portion of anal fin and/or tail tip may relate to the benefit of a hardened tail fin. In the family Ophichthidae , such black fin species are recognized in Echelus Rafinesque, 1810 , Ophichthus , Myrophis Lütken, 1852 , Neenchelys Bamber, 1915 , Scolecenchelys Ogilby, 1897 and Pylorobranchus McCosker & Chen 2013 . Although we do not have the information suggesting the hypothesis by McCosker et al. (2012), all of the Ophichthus in Table 2 are collected from deepwater. In addition, most of blackened species belonging to other genera inhabit deepwater more than about 200 m.

Other material examined. Ophichthus aniptocheilos : MNHN 2001-1061, holotype, 142 mm TL, Tonga, 391–421 m depth. Ophichthus brachynotopterus : MNHN 1979-21, holotype, 435 mm TL, Nosy-Bé, Madagascar, 355–428 m depth; MNHN 1979-22, paratype, 441 mm TL, MNHN 1979-23, paratype, 411 mm TL, collected with the holotype; NTUM 11890, 393 mm TL, sexuality unknown, Papua New Guinea region, 425–442 m depth, French beam trawl, 28 Aug. 2014, collected by J.-N. Chen. Ophichthus exourus : MNHN 1995-425, holotype, 590 mm TL, New Caledonia, 520 m depth; OCF-P03211, 634 mm TL, Okinawa, Japan. Ophichthus kunaloa : CAS 29136, holotype, 438 mm TL, Oahu, Hawaii Islands, 350 m depth. Ophichthus tomioi : CAS 214208, holotype, 386 mm TL, San Bernadino Strait, Philippine Islands, 376–382 m depth; NTUM 11891, 471 mm TL, sexuality unknown, Papua New Guinea region, 425–442 m depth, French beam trawl, 28 Aug. 2014, collected by J.-N. Chen. Ophichthus mystacinus : MNHN 1998-46, holotype, 426 mm TL, New Caledonia, 580 m depth; NTUM 11892, 2 specimens, 238–314 mm TL, sexuality unknown, Papua New Guinea region, 333–420 m depth, French beam trawl, 24 Apr. 2014, collected by J.-N. Chen.

Figures

FIGURE 6. Preserved condition of Ophichthus brevidorsalis sp. nov., ASIZP 61648, holotype, 398 mm TL, New Caledonia. A, dorsal image; B, ventral image. Arrow indicates origin of dorsal fin.

FIGURE 7. A, lateral view of head of Ophichthus brevidorsalis sp. nov., ASIZP 61648, holotype, 398 mm TL, New Caledonia (right side); B, arrangement of teeth on maxilla, palatal area; and C, mandible of Ophichthus brevidorsalis sp. nov. Arrows indicate interorbital (right) and mid-temporal (left) pores.

FIGURE 8. NJ tree based on COI sequences, constructed using the specimens mentioned in the present study. The bar indicates the evolutionary distances which were computed using the Kimura 2-parameter method.

Tables

TABLE 3. List of accession numbers of the five species of Ophichthus with dark-tipped anal fin in this study.

Specimen No.	Scientific name	Survey	Station/Gathering	Accession number
NTUM11890	O. brachynotopterus	KAVIENG 2014	CP4420	MK391546
NTUM11891	O. tomioi	KAVIENG 2014	CP4420	MK391547
NTUM11892-1	O. mystacinus	KAVIENG 2014	CP4255	MK391548
NTUM11892-2	O. mystacinus	KAVIENG 2014	CP4255	MK391549
OCF-P03211	O. exourus	-	-	MK584630
TOU-AE6871	O. megalops	-	-	MK391550
TOU-AE6872	O. megalops	-	-	MK391551
TOU-AE6874	O. megalops	-	-	MK391552
TOU-AE6875	O. megalops	-	-	MK391553
TOU-AE6877	O. megalops	-	-	MK391554
TOU-AE6878	O. megalops	-	-	MK391555
TOU-AE7153	O. megalops	-	-	MK391556

TABLE 4. Matrix of Kimura-2-parameter distances of the 13 COI sequences used to construct NJ tree in the present study. (1) to (12) are 12 specimens of five Ophichthus congeners with dark-tipped anal fin, and (13) was taken as an outgroup, respectively

	(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)	(11)	(12)	(13)
(1) O. brachynotopterus (NTUM11890)
(2) O. tomioi (NTUM11891)	0.143
(3) O. mystacinus (NTUM11892-1)	0.032	0.143
(4) O. mystacinus (NTUM11892-2)	0.032	0.143	0.000
(5) O. megalops (TOU-AE6871)	0.134	0.105	0.119	0.119
(6) O. megalops (TOU-AE6872)	0.140	0.113	0.122	0.122	0.009
(7) O. megalops (TOU-AE6874)	0.140	0.115	0.124	0.124	0.007	0.002
(8) O. megalops (TOU-AE6875)	0.139	0.114	0.124	0.124	0.007	0.002	0.000
(9) O. megalops (TOU-AE6877)	0.143	0.111	0.125	0.125	0.007	0.006	0.004	0.004
(10) O. megalops (TOU-AE6878)	0.137	0.112	0.121	0.121	0.005	0.007	0.005	0.005	0.006
(11) O. megalops (TOU-AE7153)	0.139	0.114	0.124	0.124	0.007	0.002	0.000	0.000	0.004	0.005
(12) O. exourus (OCF-P03211)	0.131	0.154	0.120	0.120	0.160	0.155	0.160	0.160	0.157	0.153	0.160
(13) Myrophis punctatus (BOLD:AAB7195)	0.189	0.194	0.173	0.173	0.183	0.191	0.184	0.183	0.193	0.186	0.183	0.185