Muraenichthys longirostris, Hibino & Ho & Mccosker, 2019

Hibino, Yusuke, Ho, Hsuan-Ching & Mccosker, John E., 2019, A new species of Muraenichthys (Anguilliformes: Ophichthidae) from Taiwan with redescription of Muraenichthys thompsoni Jordan & Richardson, 1908, Zootaxa 4702 (1), pp. 41-48 : 42-44

Muraenichthys longirostris sp. nov.

(Slender-snout worm eel) (Þḓƃǿ)

Holotype. NMMB-P 24388, 206 mm TL, off Dong-gang , Pingtung, southwestern Taiwan, 24 August 2016, bottom trawl, collected by H.-C. Ho from a fish landing ground.

Diagnosis. A species of Muraenichthys having a slender snout, its length 18% HL, with the following combination of characters: head 11% TL, tail 67% TL; dorsal-fin origin anterior to a vertical through mid-anus, horizontal distance from the vertical to the origin 113% HL; teeth relatively slender, uniserial on maxilla and vomer; predorsal vertebrae 23, preanal 41 and total 131.

Description. Counts and measurements (in mm) of the holotype: predorsal vertebrae 23; preanal vertebrae 41; total vertebrae 131; preanal lateral-line pores 42. Total length 206; head length 23.3; trunk length 45.5; tail length 137.3; predorsal length 40.9; body depth at gill opening 6.6; body depth at mid-anus 6.7; body width at gill opening 5.8; body width at mid-anus 5.9; dorsal-fin origin to anus 26.1; upper-jaw length 10.3; length of mouth gape 9.4; snout length 4.2; snout tip to tip of lower jaw 1.3; eye diameter 1.9; interorbital width 2.3; gill-opening length 1.6. Body long, subcylindrical, its depth at gill opening 31.2 in TL ( Fig. 1 ); tail compressed posteriorly, its depth weakly reduced gradually.

Head moderately large, branchial basket slightly expanded; head 8.8, and head and trunk 3.0 in TL; snout relatively long and slender, tip relatively acute, its length more than twice eye diameter; ventral groove on snout absent; lower jaw included in upper jaw, its tip beyond anterior base of anterior-nostril tube; mouth large, rictus well behind a vertical from posterior margin of eye and slightly behind a vertical through last infraorbital pore, along with a groove reaching to end of jaw; eye moderate in size, 5.4 in upper jaw and 12.3 in HL, covered by a transparent skin; mid-eye located above mid-jaw (mid-point between tip of snout and end of maxilla); anterior nostril a simple ventrally projected tube, its length half of eye diameter, its opening with a very low rim; inner opening of posterior nostril above upper lip, and outer opening oblique and outside the mouth; rim of outer opening projected ventrally; lips mostly smooth with scattered papillae on upper lip; interorbital region smooth, slightly convex; gill opening constricted, located ventrolaterally.

Dorsal and anal fins low, slightly elevated in posterior region of tail, ending confluent with caudal fin; dorsal fin originating at about 2/5 of trunk; caudal fin prominent and tip rounded; pectoral fin absent.

Head pores small but obvious; arrangement of sensory pores on head as follows ( Fig. 2A ): one + four on supraorbital; three + two on infraorbital, one between anterior and posterior nostrils; six on mandible and three on preopercle; midtemporal and interorbital pores present.

Lateral-line developed, sensory canal reaching middle portion of tail, 11 in branchial basket, 23 anterior to dorsal-fin origin, 42 anterior to anus, and 80 in total.

Teeth ( Fig. 2B, C ) moderate in size, conical, pointed, relatively slender; teeth on maxilla and vomer uniserial; teeth on mandible mostly uniserial with an additional tooth at each inner side around the symphysis; seven plus three intermaxillary teeth form an oval cluster, the anterior margin arranged in a circular pattern.

Color ( Fig. 1 ) (preserved in 50% isopropyl alcohol) of head and body brown, lower half of head to anterior tail region relatively paler. Dorsal and anal fins pale whitish brown, becoming darker before tail tip; caudal fin dark brown.

Distribution. Known only from the holotype, from off southwestern Taiwan.

Etymology. From the Latin, longirostris , in reference to the snout shape.

Remarks. The new species can be easily distinguished from all congeners by its slender and long snout (18% HL vs. 8.4–15.5% HL). The snout shape is similar to that of members of the genus Scolecenchelys Ogilby, 1897 . The position of the dorsal-fin origin overlaps with that of M. thompsoni . The former can be separated from the latter by the snout shape and length (vs. 9.5–14% HL) and its longer tail (67% TL vs. 57–64% TL).

Hibino & Kimura (2015) defined the eye of the congeners of Muraenichthys as located anterior to mid-jaw, but the position of the eye of the present species is just mid-jaw (mid-point between tip of the snout and end of maxilla). Except for these, our new species agrees well with all other diagnostic characters of Muraenichthys . In addition, the location of the orbit (from x-ray photo) corresponds with that of other Muraenichthys . Therefore, we recognized the new species as a species of Muraenichthys , and the character of the eye location is expanded from “eyes located anterior to mid-jaw” to “mid-eye located anterior to or just above mid-jaw” for the genus.

Figures

FIGURE 1. Preserved condition of Muraenichthys longirostris sp. nov., NMMB-P24388, holotype, 206 mm TL, Dong-gang, Pingtung, southern Taiwan.

FIGURE 2. Line drawings of Muraenichthys longirostris sp. nov. A, lateral view of head with sensory pores; B, teeth on maxilla and palatal area; C, teeth on mandible. IPN, inner opening of posterior nostril [inner hole in Hibino & Kimura (2015)]; OPN, outer opening of posterior nostril [outer hole in Hibino & Kimura (2015)]. Arrows indicate first mandibular (left), frontal (middle) and mid-temporal (right) pores.