Nezumia Jordan, 1904

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 243

Genus Nezumia Jordan in Jordan & Starks, 1904

[Japanese name: Nezumidara-zoku]

[?] Macruroplus Bleeker, 1874:369 (type species: Macrourus serratus Lowe, 1843 , by original designation). [See also Iwamoto (1990:248).]

Nezumia Jordan in Jordan & Starks, 1904:620 (type species: Nezumia condylura Jordan & Gilbert in Jordan & Starks, 1904, by original designation).

Diagnosis. Anus closer to pelvic-fin bases than to anal-fin origin; periproct teardrop-shaped, narrow to moderately broad. Small dermal window of light organ between pelvic-fin bases. Infraorbital ridge not connected with preopercular ridge, separated by distinct gap. Second spinous ray of first dorsal fin serrated along its leading edge. Ventral aspects of body not positioned forward, and anal-fin origin below or posterior to hind margin of first dorsal-fin base. Chin barbel present. Teeth small, in narrow to broad bands in both jaws; premaxillary band ending anterior to posterior edge of maxillary process. Tip and lateral angles of snout armed with prominent scutes. Suborbital shelf formed of stout, coarsely modified scales. Underside of snout variously naked. Spinules on body scales needle-like, triangular, or lanceolate; buttresses of spinules rudimentary; reticulate structure developed on posterior parts of unexposed portion. Grooved lateral line present (rarely interrupted anteriorly). Cephalic sensory pores usually present. Branchiostegal rays 7 (rarely 6). Body dark to dusky, lacking silvery reflection when fresh. [Modified from Sazonov & Iwamoto (1992) and Iwamoto & Williams (1999).]

Remarks. Nezumia comprises about 50 species (Iwamoto et al. 2015; this study), seven of which, including one new species, are herein recorded from Japan and adjacent waters. Some species may well be transferred to other genera if more closely studied ( Iwamoto & Williams 1999; Iwamoto et al. 2015), and a thorough phylogenetic analysis of the seven-branchiostegal-rayed grenadiers is needed to address their generic placements. The genus shows great abundance in temperate to subtemperate areas of the world’s oceans ( Iwamoto & Merrett 1997; Nakayama & Endo 2015), with the highest diversity in the eastern Pacific (10 species; Merrett & Iwamoto 2000: table 4).

Key to species of Nezumia from Japan and adjacent waters

1a Pelvic-fin rays 13–17 ........................................................... 2

1b Pelvic-fin rays 8–11 ............................................................. 3

2a Snout length less than orbit diameter; transverse scale rows below second dorsal-fin origin 10–12.5; body scales covered with needle-like spinules in discrete parallel to slightly convergent rows ................................................ N. condylura

2b Snout length longer than orbit diameter; transverse scale rows below second dorsal-fin origin 7.5; body scales covered with narrowly lanceolate spinules in tightly packed convergent rows................................................................. N. kamoharai

3a Snout barely protruding beyond upper jaw, its ventral contour almost vertical ...................................................................... 4

3b Snout protruding well beyond upper jaw, its ventral contour oblique.................................................................................. 5

4a Transverse scale rows below second dorsal-fin origin 9–10; orbit–preopercle distance 39–41% HL; interorbital width 20–22% HL; pelvic-fin length 46–54% HL; length of gill slit 13–16% HL ................................................... N. rara sp. nov.

4b Transverse scale rows below second dorsal-fin origin 8.5; orbit–preopercle distance 42–43% HL; interorbital width 23– 25% HL; pelvic-fin length 69% HL; length of gill slit 17–18% HL .................................................................... N. tomiyamai

5a Underside of head mostly scaled, naked areas confined to underside of snout and anterior portions of mandibular rami; spinules on body scales lanceolate....................... N. proxima

5b Underside of head completely naked including mandibular rami; spinules on body scales needle-like............................ 6

6a Pelvic-fin rays 10; spinules on body scales arranged in discrete parallel rows; second spinous ray of first dorsal fin not especially prolonged, height of first dorsal fin about equal to HL ............................................................... N. shinoharai

6b Pelvic-fin rays 8; spinules on body scales densely scattered over exposed portion; second spinous ray of first dorsal fin greatly prolonged, height of first dorsal fin distinctly longer than HL.................................................................. N. spinosa