Ventrifossa Gilbert & Hubbs, 1920

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 284-285

Genus Ventrifossa Gilbert & Hubbs, 1920

[Japanese name: Misaki-sokodara-zoku]

Ventrifossa Gilbert & Hubbs, 1920:543 (type species: Coryphaenoides garmani Jordan & Gilbert in Jordan & Starks, 1904, by original designation).

Atherodus Gilbert & Hubbs, 1920:544 (subgenus of Ventrifossa ; type species: Optonurus atherodon Gilbert & Cramer, 1897 , by original designation).

Lucigadella Gilbert & Hubbs, 1920:552 (subgenus of Ventrifossa ; type species: Macrourus nigromarginatus Smith & Radcliffe in Radcliffe, 1912, by original designation).

Sokodara Iwamoto, 1979:153 (subgenus of Ventrifossa ; type species: Coryphaenoides misakius Jordan & Gilbert in Jordan & Starks, 1904, by original designation).

Diagnosis. Anus closer to pelvic-fin bases than to anal-fin origin; periproct teardrop-shaped, narrowly developed. Small dermal window of light organ between pelvic-fin bases. Infraorbital ridge not connected with preopercular ridge, separated by distinct gap. Leading edge of second spinous ray of first dorsal fin smooth or serrated. Pelvic fin inserted below or anterior to pectoral-fin base. Chin barbel well developed. Premaxillary teeth in narrow tapered band, with outer series enlarged; posterior margin of premaxillary tooth band extending beyond hind edge of maxillary process; mandibular teeth small, in 2–3 rows or narrow band. Spinules on body scales needle-like or broadly triangular, arranged in quincunx order; buttresses of spinules scarcely developed; reticulate structure absent. Head fully covered with small, unmodified scales; snout tipped with small modified scute in some species (subgenus Sokodara Iwamoto, 1979 ). Grooved lateral line present. Cephalic sensory canals lacking open pores. Pyloric caeca numerous, about 30–75. Branchiostegal rays 7. Body dark to swarthy, with silvery reflection when fresh in most species. [Modified from Sazonov & Iwamoto (1992), Iwamoto & Merrett (1997), and Iwamoto & Graham (2001).]

Remarks. Ventrifossa includes more than 25 species ( Iwamoto & Graham 2001), eight of which are herein recorded from the study area. Iwamoto & Williams (1999:219) noted the absence of synapomorphies uniting all the species of the genus. Four subgenera were previously recognized ( Iwamoto 1979): Atherodus Gilbert & Hubbs, 1920 ; Lucigadus Gilbert & Hubbs, 1920 ; Sokodara Iwamoto, 1979 ; and Ventrifossa . Of these, Lucigadus now deserves full generic status (see the Remarks of that taxon). Generally, most species of Ventrifossa are too similar to one another to allow ready identification in the field. In addition, almost intact specimens are often needed for reliable identification to the species level (Iwamoto et al. 2015). According to Iwamoto (1990:292), the genus is most similar to Malacocephalus G̹nther, 1862.

Key to species of Ventrifossa from Japan and adjacent waters

1a Second spinous ray of first dorsal fin smooth along its leading edge; outer series of premaxillary tooth band distinctly enlarged; mandibular teeth arranged in 2 irregular rows ....... ......................................................................... V. macroptera

1b Second spinous ray of first dorsal fin serrated along its leading edge; outer series of premaxillary tooth band only slightly enlarged ................................................................................ 2

2a Snout moderately high, protruding distinctly beyond upper jaw; suborbital shelf abruptly and greatly constricted anteriorly; small but prominent tubercular scute at tip of snout; barbel short, length 3–16% HL (usually ±12%); body scales very small, longitudinal scales over distance equal to predorsal length 58–73......................................................... 3

2b Snout low, protruding only slightly beyond upper jaw; suborbital shelf not greatly constricted anteriorly; no scutelike scales at tip of snout; barbel well developed, length 16– 38% HL; body scales moderately small, longitudinal scales over distance equal to predorsal length 35–56..................... 4

3a Oral cavity black; barbel length 9–16% HL; internasal width 21–23% HL .................................................. V. johnboborum

3b Oral cavity pale; barbel length 3–7% HL; internasal width 24–29% HL ........................................................... V. misakia

4a Body scales available for identification ............................... 5

4b Body scales not available for identification......................... 6

5a Spinules on body scales broadly triangular........ * V. garmani

5b Spinules on body scales needle-like..................................... 6

6a Transverse scale rows below second dorsal-fin origin 8.5– 11.5................................................................ V. longibarbata

6b Transverse scale rows below second dorsal-fin origin 6–7.5 7

7a Prominent black spot on first dorsal fin............................... 8

7b First dorsal fin uniformly dusky........................................... 9

8a Anal fin immaculate anteriorly; interorbital width 27–29% HL; upper-jaw length 38–40% HL; inner gill rakers on second arch 12–13.................................................... V. nigrodorsalis

8b Anal fin narrowly black along anterodistal margin; interorbital width 20–27% HL; upper-jaw length 42–47% HL; inner gill rakers on second arch 14–18..................... V. rhipidodorsalis

9a Snout width 25–29% HL; suborbital width 11–13% HL....... ............................................................................ * V. garmani

9b Snout width 30–40% HL; suborbital width 13–17% HL........ .......................................................................... V. saikaiensis