Chauligenion McCosker and Okamoto

McCosker, John E. & Okamoto, Makoto, 2016, Chauligenion camelopardalis, a New Genus and Species of Deepwater Snake Eel (Anguilliformes: Ophichthidae) from the East China Sea, Proceedings of the California Academy of Sciences 63 (9), pp. 321-328 : 322-326

Genus Chauligenion McCosker and Okamoto , novum

(New Japanese name: Kirin-umihebi-zoku)

Type species: Chauligenion camelopardalis McCosker & Okamoto 2016 , by original designation.

( Figures 1–6 )

DIAGNOSIS.— An elongate ophichthine with tail longer than head and trunk, body cylindrical, becoming laterally compressed in tail region; snout and tail tip pointed; lower jaw slightly extended; anterior nostril a hole above outer lip, without a tube; posterior nostrils along upper lip; jaws elongate, capable of closing completely; orbit large, in posterior half of upper jaw, its rear margin above rictus; gill openings low lateral, vertical; median fins elongate, not elevated; dorsal-fin origin above gill opening; pectoral fins absent; teeth small, conical, numerous and densely packed; preopercular pores 3; coloration yellowish-tan overlain with rows of brown spots.

DESCRIPTION (other characters those of the single species).— An elongate ( Fig. 1 ) ophichthine, with tail longer than head and trunk, cylindrical in head and trunk, becoming laterally compressed in tail region. Snout acute, pointed, its underside not split. Lower jaw slightly in advance of snout tip. Branchial basket moderately expanded. Anterior nostrils above outer lip, without a tube; posterior nostrils along upper lip, not opening into mouth, not visible externally. Jaws elongate, capable of closing completely; orbit large, in posterior half of upper jaw, its rear margin in advance of the rictus. Lips smooth, without crenulae or barbels. Gill openings low lateral ( Fig. 2 ), vertical, not converging forward, opening about twice eye diameter. Median fins elongate, not elevated, entering tail well in advance of pointed tail tip. Dorsal-fin origin above gill opening. Pectoral fins absent. Cephalic and lateral-line pores developed, supraorbital (S0), infraorbital (IO), preoperculomandibular (POP) and medi- an supratemporal pore (ST) and interorbital pores present. Teeth small, conical, numerous and densely packed. Anterior ethmovomerine teeth the largest, slightly retrorse, followed by 6–7 irregular rows of smaller teeth, followed by a row of 25 smaller vomerine teeth. Teeth of maxillary and mandibular in patches, becoming smaller and more numerous posteriorly. Gill arches ( Fig. 3 ) mostly cartilaginous: basibranchials 1–4 cartilaginous; hypobranchials 1–4 cartilaginous; ceratobranchial 1 cartilaginous, 2–4 ossified, 5 minute and cartilaginous; epibranchial 1 cartilaginous, 2–4 ossified; infrapharyngobranchials 2–3 ossified; upper and lower pharyngeal tooth plates with 5 nearly regular rows of small, conical, densely packed and slightly retrorse teeth, the upper pharyngeal tooth plate with 5 longitudinal rows of ca. 15 teeth, plates closely sutured but not fused; the lower pharyngeal tooth plate with 20–25 conical teeth in 5 irregular longitudinal rows. Teeth comparable in size and appearance to those of jaws.Neurocranium depressed ( Fig. 4 ). Supraoccipital condyle developed. Suspensorium nearly vertical; maxillae not tapering posteriorly. Opercle and preopercle weakly developed. Branchiostegal rays slender, condition typically ophichthine (sensu McCosker 1977: 28–30), ca. 20–25 (as seen by radiograph to be) attached to outer face of each epihyal. Pectoral girdle reduced to cleithrum and thin supracleithrum.Epipleural ribs attached to precaudal vertebrae 5–11 are elongate. Other characters those of the single species.

DISTRIBUTION.— Known only from the type specimen, collected by trawl in 150 m from the East China Sea .

ETYMOLOGY.— From the Greek chaulios (prominent) and genion (chin), neuter, in reference to its obtrusive lower jaw tip.

REMARKS.— In that the new genus and species is known only from a single specimen, we were unable to prepare a cleared-and-stained specimen and therefore were unable to make a complete osteological examination. The holotype was preserved in formalin soon after capture and fresh tissue was not removed, making a genomic comparison impossible at this time. We look forward to additional fresh material so that those studies can be performed.

We were able however, based on its morphometry, meristics, and the removal of its gill arches, to make some conclusions as to its similarity to other ophichthids. It is clearly within the subfamily Ophichthinae based on its hard-pointed tail tip (without caudal rays), its frontal and temporal canals, its gill arch condition, and the location of its branchiostegal rays ( McCosker 1977). Its other characteristics are so unique that we are unable to confidently place Chauligenion camelopardalis within any of the currently recognized tribes. We would exclude it from the tribe Callelchelyini which has a body greater than its tail length, low lateral gill openings, a dorsal fin arising above the nape, and a short and posterior-sloping neurocranium. They too lack pectoral fins, however their pectoral girdle is somewhat simpler. The species of Sphagebranchini are similar in body/tail proportions to the new species, however their gill-opening location is entirely ventral and converging forward, their neurocranium is elongate, and depressed and truncate posteriorly, and their coloration is generally without markings and nearly uniform. The species of Bascanichthyini are similar in their gill-opening location, their body is usually longer than the tail, their dorsal fin usually arises on the head, they lack the third preopercular pore and the fifth ceratobranchial, and their coloration is nearly uniform. The species of the tribe Ophichthini , the most numerous within the family, are the most variable of ophichthids. The new species is similar to many ophichthines in some of its characteristics, but it is unique among them in lacking a pectoral fin and in the location and shape of its posterior nostril. The condition of its extended lower jaw is also unique. Whereas species of other ophichthin genera ( Echiophis , Brachysomophis , and Aplatophis ) also have lower jaws extending beyond their snouts, those species all possess pectoral fins, slender, fewer, and longer teeth, and are more robust. Species of Herpetoichthys and Quassiremus are similar in general appearance (boldly spotted), but they too are stouter and have small pectoral fins and have fewer and more slender teeth. The new species is similar to species of Xyrias in the size and distribution of its maxillary dentition, and in its snout shape, anterior nostril condition, and spotted appearance, however it differs from all of them in lacking a pectoral fin and in other anatomical characters (cf. McCosker et al. 2009).

The gill arch condition of Chauligenion camelopardalis deserves special mention. It is clearly that of an ophichthid ( Nelson 1966; McCosker 1977), albeit some elements are reduced from bone to cartilage. Ophichthids are unique among anguilliforms ( McCosker et al. 1989) in having: a cartilaginous connection between the proximal ends of the dorsal parts of the first and second gill arches; the first basibranchial either ossified or absent, all others are cartilaginous, rudimentary, or absent; hypobranchials 1–2 ossified; the second infrapharyngobranchial is ossified; and, members of the subfamily Ophichthinae possess or have reduced or lost the fifth ceratobranchial, whereas those of the Myrophinae have lost it. Chauligenion camelopardalis satisfies all of those conditions.

Figures

FIGURE 1.Holotype of Chauligenion camelopardalis sp. nov., NSMT-P 125489, female, 407 mm TL, photographed soon after capture and before preservation. Arrows indicate origin of dorsal and anal fins.

FIGURE 2. Head of holotype of Chauligenion camelopardalis sp. nov., NSMT-P 125489, female, 407 mm TL, photographed soon after capture and before preservation.

FIGURE 3. Gill arches (interior view, cut longitudinally along dorsal surface and spread laterally) of holotype of Chauligenion camelopardalis sp. nov., NSMT-P 125489, female, 407 mm TL. Bone is stained red and cartilage is blue.

FIGURE 4. Radiograph of head of holotype of Chauligenion camelopardalis sp. nov., NSMT-P 125489, female, 407 mm TL.

FIGURE 5. Schematic illustration of head of holotype of Chauligenion camelopardalis sp. nov., NSMT-P 125489, female, 407 mm TL.

FIGURE 6. Schematic illustration of dentition (upper jaw left, lower jaw right) of holotype of Chauligenion camelopardalis sp. nov., NSMT-P 125489, female, 407 mm TL.