Benthocometes australiensis Nielsen, 2010

Mizumachi, Kaito & Endo, Hiromitsu, 2019, New Japanese Record of the Rare Cusk Eel Benthocometes australiensis (Actinopterygii: Ophidiiformes: Ophidiidae), a First Record of the Species from the Northern Hemisphere, Species Diversity 24 (1), pp. 7-10 : 7-9

Benthocometes australiensis Nielsen, 2010

[New standard Japanese name: Muroto-suisei-ashiro]

( Figs 1 , 2 ; Table 1 )

Benthocometes australiensis Nielsen, 2010: 59 (original description; holotype: NMV A 29728 -016 ; type locality: off northwestern Australia, 390–394 m depth).

Material examined. BSKU 117791, 114.4 mm SL, 33°17′38.0″N, 134°13′34.3″E, off eastern side of Cape Muroto , Kochi Prefecture, Shikoku Island, Japan, 320 m depth, pumped up together with deep seawater, collected by Kochi Prefectural Deep Seawater Laboratory, 4 April 2006 .

Diagnosis. Long gill rakers on anterior arch 3; predorsal pterygiophores 4; teeth patch on palatine circular; predorsal length 17.7–22.0% of SL; upper jaw length 8.0–8.7% of SL; dorsal-fin origin above 3rd vertebra; anal-fin origin below bases of 24th–28th dorsal-fin rays; all teeth on jaws conical, canine-like; distinct supraorbital pores [Modified from Nielsen (2010)].

Description of Japanese specimen. Selected counts and measurements are given in Table 1 . Body short, compressed, robust. Head relatively small, its length 47.8% of preanal length. Head and body fully covered with small scales (size of each scale under pectoral fin about 1.7 mm in diameter). Lateral line distinct and short, ending a head-length from caudal-fin base, its length 65.6% of SL. Snout short, its length 23.1% of HL. Eyes relatively large, diameter 24.7% of HL. Mouth small, posterior end of maxilla below middle of eye. Anterior nostril with short tube. Posterior nostril larger than anterior, without tube, adjoining eye. Tip of snout with about 20 small, black skin flaps. Opercle with 2 strong and sharp spines. Origin of dorsal fin anterior to a vertical from pectoral-fin base. Anal-fin origin slightly anterior to horizontal mid-point of body, located below 14th vertebra. Pelvic fin originating below dorsal-fin origin, its tip below middle of pectoral fin. Caudal fin connected with dorsal and anal fins. Fin membrane of vertical and pectoral fins thin. Anterior gill arch with 2–3 small, spiny knobs on upper branch; lower branch with 3 long rakers and 7 small, spiny knobs. Cephalic sensory canals with open pores; number of pores in supraorbital row 3, infraorbital row 5, mandibular row 3 and preopercular row 2. All conical teeth small, canine-like, curved. Vomerine tooth patch small, circular, with 12 teeth. Palatine tooth patch short, oval, with about 20 teeth. Teeth on premaxilla with 2 rows near symphysis, 1 row posteriorly. Teeth on lower jaw with 2–3 rows near symphysis, 1 row posteriorly.

Axial skeleton (based on radiographs; Fig. 2 ). First neural spine short, half length of second spine. 1st–7th precaudal vertebrae with pointed neural spines. 8th–12th precaudal vertebrae with relatively blunt neural spines and all caudal neural spines with pointed tips. Haemal spines of precaudal vertebrae with pointed tips. Neural spines on precaudal vertebrae, 5th–12th with enlarged bases. Parapophyses on 6th–12th vertebrae increasing in width and length toward 12th one. Pleural ribs on 3rd–12th vertebrae. First predorsal pterygiophores above 1st vertebra.

Color in alcohol ( Fig. 1 ). Ground color of head and body brown with numerous small black spots on head, pectoral fin and abdomen. Fin membrane of vertical and pectoral fins translucent. Vertical fins with numerous small brown spots. Lower jaw relatively pale, around symphysis blackish. Inside of operculum densely covered with melanophores. Lateral line pale.

Distribution. Known from the southeastern Indian Ocean off northwestern Australia (type locality; Nielsen 2010) and the northwestern Pacific off southwestern Japan (this study), at depths of 320– 394 m.

Remarks. The Japanese specimen identified as a species of Benthocometes is clearly distinguished from other ophidiid genera by the following combination of characters: 2 posteriorly directed opercle spines, 3 long gill rakers, 7 pseudobranchial filaments, 4 predorsal pterygiophores, a blunt snout, and diameter of eye larger than snout length ( Nielsen et al. 1999; Nielsen 2010; this study). Nielsen (2010) reported that the two valid species of Benthocometes , B. robustus and B. australiensis , can be distinguished from each other by the numbers of long gill rakers on the anterior arch (3 in B. australiensis vs. 9–12 in B. robustus ) and predorsal pterygiophores (4 vs. 7–10), form of palatine dentition (circular vs. elongate), predorsal length (22.0% vs. 26.5–31.0% SL), upper jaw length (8.7% vs. 11.0–13.0% SL), position of dorsal-fin origin (above 3rd vs. 6th–7th vertebrae), position of anal-fin origin (below 24th vs. 17th–20th dorsal-fin rays), form of teeth (large canine-like teeth vs. small granular teeth), and supraorbital pores (developed vs. undeveloped). These characters of the Japanese specimen agree well with those of B. australiensis given by Nielsen (2010) except the position of the anal-fin origin, which is located below the base of 28th dorsal-fin ray in the Japanese specimen but below the base of 24th dorsal-fin ray in the holotype. According to Nielsen (2010), this character’s interspecific range in B. robustus is four, and we therefore regard this slight difference in the position of the anal-fin origin (below bases of 24th–28th dorsal-fin rays) as intraspecific variation.

Benthocometes australiensis was described by Nielsen (2010) based on the 93 mm SL holotype collected from off northwestern Australia . The Japanese specimen is the second record of B. australiensis , and the first record from the Northern Hemisphere . In addition, based on the specimen BSKU 117791 , the new standard Japanese names, “Suiseiashiro-zoku” and “Muroto-suisei-ashiro,” are proposed for the genus and species, respectively . These names are derived from part of the generic name, “ comet ” (= Suisei), the Japanese name for ophidiids (= Ashiro ), and the locality of the Japanese specimen (= Muroto) .

Figures

Fig. 1. Benthocometes australiensis, BSKU 117791, 114.4mm SL. Preserved condition.

Fig. 2. Soft x-ray image of Benthocometes australiensis, BSKU 117791, 114.4mm SL.