Nezumia kamoharai Okamura, 1970

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 248-249

Nezumia kamoharai Okamura, 1970

[Japanese name: Sokodara ]

( Figs. 166–167 ; Appendix 3-10B)

Nezumia kamoharai Okamura, 1970a:91 , pl. XX, text-fig. 40 (original description; holotype: BSKU 14202, from Sagami Bay; new Japanese name: “Soko-dara”); Okamura 1970b: table 1 (listed; Japan); Tominaga & Uyeno 1981:489 (listed; Japan); Okamura 1984b:94, pl. 344, fig. K (compiled); Okamura 1988:94, pl. 344, fig. K (compiled); Nakabo 1993:361 (in key; Japan); Nakabo 2000:425 (in key; Japan); Nakabo 2002:425 (in key; Japan); Senou et al. 2006:421 (listed; Sagami Sea); Nakabo & Kai 2013:501 (in key; Japan); Motomura 2020:39 (listed; Japan).

Diagnosis. A species of Nezumia with 13 pelvic-fin rays. Snout moderately long, conical, protruding distinctly beyond upper jaw, length 30% HL, ventral contour oblique in lateral view; underside of snout completely naked; ventral surfaces of head mostly scaled posterior to vertical through midorbit; mandibular rami naked, with narrow scaly patches on posterior portions; barbel length 12% HL. Second spinous ray of first dorsal fin not extremely prolonged (height of fin 99% HL). Body scales covered with short, greatly reclined, narrowly lanceolate spinules in tightly packed convergent rows; tip of last spinule in each row extending slightly beyond posterior scale margin; middle row of spinules distinctly larger than adjacent rows; scales below second dorsal-fin origin 7.5. Cephalic sensory pores present; those on mandibular and infraorbital canals small but conspicuous. No prominent dark band encircling trunk; first dorsal fin without black blotch apically.

Material examined. 1 specimen. Holotype of Nezumia kamoharai: BSKU 14202 (1, 62.4 mm HL, 350+ mm TL), Sagami Bay , Kanagawa Pref., Japan, 1967.

Counts and measurements. Counts: first dorsal-fin rays II,9; pectoral-fin rays i19–i21; pelvic-fin rays 13; gill rakers on first arch (outer/inner) 8–9/10, on second arch 9/11; longitudinal scales 36; transverse scale rows below first dorsal-fin origin 10, below first dorsal-fin midbase 7.5, below second dorsal-fin origin 7.5, above anal-fin origin 25.5.

The following measurements are in % of HL, followed by those in % of PRL in parentheses: snout length 30 (41); orbit diameter 28 (39); postorbital length 46 (64); postrostral length 73; orbit–preopercle distance 39 (53); suborbital width 15 (21); upper-jaw length 30 (41); length of rictus 24 (33); length of premaxillary tooth band 18 (24); preoral length 25 (34); distance between tip and lateral angle of snout 18 (25); snout width 27 (37); internasal width 21 (29); interorbital width 21 (29); body width over pectoral-fin bases 57 (78); body depth at first dorsal-fin origin 82 (112); body depth at anal-fin origin 69 (95); prepelvic length 116 (160); preanus length 135 (185); preanal length 153 (210); isthmus–pelvic distance 38 (52); isthmus–anus distance 57 (78); isthmus–anal distance 74 (101); pelvic–anal distance 42 (58); anusanal distance 18 (25); pelvic-fin length 44 (60); pectoralfin length 50 (68); predorsal length 115 (158); height of first dorsal fin 99 (135); length of first dorsal-fin base 26 (36); interdorsal length 35 (49); length of gill slit 14 (19); length of posterior nostril 4 (5); barbel length 12 (16).

Size. To at least 35 cm TL.

Distribution. So far known only from Sagami Bay (Appendix 3-10B). Depth unknown. Very rare.

Remarks. For a full description see the original description given by Okamura (1970a). Nezumia kamoharai was described from a single specimen collected from Sagami Bay ( Fig. 166 ). The holotype is the only representative of this rare species and, despite intensive sampling efforts in southern Japan, no additional specimens have been collected since the original description.

Relationships and comparisons. Nezumia kamoharai is unlikely to be confused with any other Japanese congeners in having 13 pelvic-fin rays, a moderately long, pointed snout (30% HL), and the middle row of body-scale spinules distinctly enlarged compared with adjacent rows ( Fig. 167 ). Elsewhere, this species appears to be most closely related to N. longebarbata ( Roule & Angel, 1933) so far known from Madeira and the Gulf of Mexico. These two species are similar to each other in having 13 pelvic-fin rays and the underside of the head broadly naked from the snout tip to a vertical at the hind rim of the orbit. However, N. kamoharai is separable from N. longebarbata by having a smaller orbit (28% HL vs. 31–32%), shorter barbel (12% HL vs. 17–23%) and pectoral fin (50% HL vs. 53–57%), and slightly larger body scales (transverse scale rows below the second dorsal-fin origin 7.5 vs. 8.8). [Data for N. longebarbata are from Marshall & Iwamoto (1973).]

In his visit to BSKU in 2009, T. Iwamoto (CAS) informed the present author that N. kamoharai also shares many features with N. obliquata ( Gilbert, 1905) , a rare species confined to the Hawaiian-Emperor Seamount Chain. The latter species was originally described from a small juvenile collected from Hawaii [USNM 51514, holotype (ca. 24 mm HL, 127+ mm TL, fide Sazonov 1994:103)], and is poorly represented in museum collections. Sazonov (1994) recorded an additional specimen of this species from Ojin Guyot in the Emperor Seamounts (ZMMGU P.18245, 60.6 mm HL, 398+ mm TL), although he considered his identification tentative due to a number of differences related to the difference in body size between the holotype and the second specimen. An examination of Sazonov’s (1994) specimen revealed its close similarity with N. kamoharai , but the holotype of N. kamoharai differs from that specimen in having shorter barbel (12% HL vs. 17%), pelvic fin (44% HL vs. 65%), and pectoral fin (50% HL vs. 59%). Spinulation of the body scales is also different between the two specimens. In the holotype of N. kamoharai , the middle row of spinules is distinctly larger than adjacent rows ( Fig. 167 ), whereas in the “ N. obliquata ” specimen from the Emperor Seamounts, the middle row is not especially enlarged ( Sazonov 1994: fig. 3). These two specimens are almost equal in size, and their differences appear to warrant specific separation. The status of Sazonov’s (1994) specimen is still uncertain, but it does not seem to represent either N. obliquata nor N. kamoharai . Based on the original description given by Gilbert (1905), the holotype of N. obliquata differs from N. kamoharai in having fewer pelvic-fin rays (12 vs. 13) and smaller body scales (9 below the second dorsal-fin origin vs. 7.5). To resolve the taxonomic status of these species, a further study should be done when more specimens become available.

Figures

FIGURE 166. Holotype of Nezumia kamoharai. BSKU 14202, 62.4 mm HL, 350+ mm TL, Sagami Bay, Pacific. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. Preserved condition. [Photos: N. Nakayama]

FIGURE 167. Scanning electron micrographs showing body scale (from the dorsum below the interdorsal space) of Nezumia kamoharai. BSKU 14202, holotype, 62.4 mm HL. (A) View from above; (B) oblique view. [Photos: NSMT]