Xyrias chioui, E, John, Chen, Wei-Li & Chen, Hong-Ming, 2009

E, John, Chen, Wei-Li & Chen, Hong-Ming, 2009, Comments on the snake-eel genus Xyrias (Anguilliformes: Ophichthidae) with the description of a new species, Zootaxa 2289, pp. 61-67 : 63-65

Xyrias chioui , new species

( Figs. 1–4 )

Holotype. TOU-AE 1561, 819 mm TL, male, Changbin (23o17'N, 121o27'E), Taitung County, Taiwan, caught on a benthic longline set upon a sand bottom at 60–70 m depth by Jiun-Shiun Chiou, Oct. 2004.

Diagnosis. A moderately elongate species of Xyrias with tail 47% and head 12% of TL; dorsal-fin origin well behind pectoral tips; pectoral fin spatulate, elongate, 5.9 in HL; snout short, 2.7 in jaw; upper jaw elongate, 2.6 in HL; center of eye in anterior 40% of upper jaw; labial cirri and barbels absent; eyes not elevated; head pores minute, supraorbital pores 1+3, infraorbital pores 4+3, preoperculomandibular pores 2+6; teeth numerous, conical, needle-like, biserial on maxilla and uniserial on mandible and vomer; coloration in preservative pale ventrally, becoming brown dorsally, pectoral fins brown, median fins with a thin dark margin. Vertebral formula 19/61/126.

Loh).

Counts and measurements (in mm) of the holotype. Total length 819; head 101; trunk 334; tail 384; predorsal distance 167; pectoral-fin length 17.1; pectoral-fin base 5.2; body depth at gill openings ~35; body width at gill openings ~23; body depth at anus ~32; body width at anus ~24; snout 14.3; tip of snout to rictus 39.0; tip of lower jaw to rictus 38.6; eye diameter 6.2; interorbital distance 6.6; gill opening height ~12; isthmus width 14.1. Vertebral formula 19/61/126. Weight before preservation 497.5 g.

Description. Body moderately elongate ( Fig. 1 ), depth at gill openings 23 in TL, nearly cylindrical for much of its length, becoming laterally compressed in posterior tail region. Head and trunk slightly longer than tail; tail 2.1 and head 8.1 in TL. Snout acute when viewed from above, its lateral profile evenly sloping to eye (Fig. 2), with a minor brow behind orbit. Jaws nearly subequal. Snout foreshortened, center of eye at anterior 40% of jaw. Jaws elongate, about 2.6 in head. Lips without cirri or barbels. Anterior nostril in upper lip in a short tube and laterally directed, ovate, with a minute flap, closely followed by posterior nostril, which opens into mouth along outer edge of lip but is entirely covered by a flap, which ends beneath anterior margin of eye. Eye small. Interorbital space flat, narrow, slightly wider than eye; a small brow exists at the intersection of dorsal-most postorbital bone and frontal bone. Median fins low (difficult to observe in preservative), ending before tail tip. Dorsal-fin origin nearly 3 pectoral-fin lengths behind pectoral-fin tips. Pectoral fins moderately elongate, about equal to distance from snout tip to rear margin of orbit, spatulate in shape. Pectoral base at 20o angle relative to body; upper edge of pectoral base attached at posterodorsal corner of gill opening, lower edge within upper 10% of gill opening. Gill openings lateral, on lower half of body. Isthmus about equal to unstretched gill opening.

Head pores ( Fig. 3 ) minute, difficult to discern, those of mandible and preopercle inconspicuous. Single median interorbital and temporal pores. Supraorbital pores 1+3, infraorbital pores 4+3, postorbital pores 3, mandibular pores 6, preopercular pores 2. Lateral-line pores inconspicuous and difficult to count.

Teeth ( Fig. 4 a) conical, slender, slightly recurved and needle-like. An anterior rosette of 10 small teeth, followed by 5 larger teeth (the fourth missing, the fifth the largest in jaw) along ethmoidal midline, these followed by a short gap, 2 teeth, a short gap, a single tooth, a short gap, and 4 shorter nearly equally spaced vomerine teeth. Maxillary teeth in biserial linear rows separated by a trough; an inner row of 16–22 evenly spaced teeth, the outer row of 24–28 more closely spaced slightly smaller teeth begins slightly posteriorly and extends further. Mandibular teeth uniserial, very linear, largest anteriorly, 22–28 on each side.

Coloration (when fresh) pale on ventral surface, becoming olive-brown above lateral midline. Throat, cheeks, lower jaw, snout and interorbital region pale brown. Five to six small white spots flank the anterior third of lower jaw. Palate and tongue dusky. Pectoral fins dark brown. Median fins pale olive basally with a thin dark-brown margin. Lateral-line pores unpigmented. Peritoneum pale.

Size. Known only from the 819 mm holotype, a male.

Distribution. Known only from the holotype, captured above a sand bottom at 60-70 m depth, off eastern Taiwan.

Etymology. Named chioui in honor of Captain Jiun-Shiun Chiou, who captured and donated this and other important eel specimens to the laboratory of the National Taiwan Ocean University.

Figures

FIGURE 1. Holotype of Xyrias chioui, TOU-AE 1561, FIGURE 2. Head of holotype of Xyrias chioui, TOU-AE 819 mm TL, soon after capture (photo by Kar-Hoe Loh). 1561, 819 mm TL, soon after capture (photo by Kar-Hoe

FIGURE 3. Diagrammatic illustration of cephalic pores and nostrils of holotype of Xyrias chioui, TOU-AE 1561, 819 mm TL. Arrows point to the median interorbital pore and the median temporal pore. Abbreviations: AN, anterior nostril; PN, posterior nostril.

FIGURE 4. Diagrammatic illustration of the dentition of the holotypes of species of Xyrias: a. holotype of X. chioui, TOU-AE 1561; b. X. guineensis, MNHN 1974 - 186 (after Blache, 1975: fig. 8); c. X. multiserialis, BMNH 1939.5. 24.649 (after Norman, 1939: fig. 15); d. X. revulsus, CAS-SU 6476 (from McCosker 1998: fig. 2).