Nezumia tomiyamai (Okamura, 1963)

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 264-266

Nezumia tomiyamai (Okamura, 1963)

[Japanese name: Tomiyama-hige]

( Figs. 172 C–D, 178–179; Table 13 ; Appendix 3-11A)

Lionurus tomiyamai Okamura, 1963a:31 , figs. 8–10 (original description, holotype ZMUT 52045 , from “off eastern coast of Japan ”; new Japanese name: “ Tomiyamahige ”).

Nezumia tomiyamai: Okamura 1970a:98 , pl. XXII, text-fig. 42 [description after Okamura (1963)]; Okamura 1970b: table 1 (listed; Japan); Tominaga & Uyeno 1981:489 (listed; Japan); Okamura 1984b:94, pl. 345, fig. B (compiled); Okamura 1988:94, pl. 345, fig. B (compiled); Nakabo 1993:360 (in key; Japan); Nakabo 2000:424 (in key; Japan); Nakabo 2002:424 (in key; Japan); Nakabo & Kai 2013:500 (in key; Japan); Amaoka et al. 2020:159, fig. 212 (photograph of holotype; erroneously listed from Hokkaido); Motomura 2020:39 (listed; Japan).

Nezumia sp .: Okamura 1982:306 (listed; 1 spec., BSKU 26116 ; Kyushu-Palau Ridge).

Diagnosis. A species of Nezumia with 10–11 pelvic-fin rays. Snout short, protruding scarcely beyond upper jaw, length 27% HL, ventral contour almost vertical in lateral view; underside of snout broadly naked; ventral surfaces of head scaled posterior to vertical through lateral angles of snout; mandibular rami mostly scaled; orbit–preopercle distance 42–43% HL; interorbital width 23–25% HL; pelvic-fin length 69% HL; length of outer gill slit 17–18% HL. Second spinous ray of first dorsal fin not extremely prolonged (height of fin 78–90% HL). Body scales covered with short, greatly reclined, narrowly triangular spinules in tightly packed convergent rows or densely scattered over exposed portion; tip of last spinule in each row extending slightly beyond posterior scale margin; middle row of spinules not enlarged; scales below second dorsal-fin origin 8.5. Cephalic sensory pores present along all canals, but barely discernible. No dark band encircling trunk; first dorsal fin uniformly blackish.

Material examined. 3 specimens. Holotype of Lionurus tomiyamai: ZMUT 52045 (58.4 mm HL, 321+ mm TL), off east coast of Japan , no further information. Non-types: Japan: BSKU 26116 (1, 58.4 mm HL, 300+ mm TL), Kyushu-Palau Ridge, 27.9033ºN, 134.6583ºE, 700 m, F/ Vs Shinsei-maru, No. 53 and Kyoyo-maru, No. 2, sta. 2-4, bottom trawl, coll. Y. Kobayashi et al., 20 Feb. 1978; HUMZ 71963 (1, 68.7 mm HL, 372+ mm TL), Shichito-Iojima Ridge, 26.6333ºN, 140.8833ºE, 580– 1100 m, 1 Nov. 1977.

Counts and measurements. See Table 13 .

Size. To about 37 cm TL ( HUMZ 71963, 372+ mm TL, Shichito-Iojima Ridge, Japan).

Distribution. So far known only from Japanese waters. Specimens associated with reliable locality information were collected from only the Kyushu-Palau and Shichito-Iojima Ridges at depths of 580‾ 1100 m (Appendix 3-11A). Very rare.

Remarks. This species was fully described by Okamura (1963a), which readers can refer to for further detail. During the course of this study, one additional specimen of this rare species was found among the HUMZ collection (HUMZ 71963, 68.7 mm HL, 372+ mm TL, from Shichito-Iojima Ridge; Fig. 179 ). Okamura et al. (1982:306) reported “ Nezumia sp.” from the Kyushu-Palau Ridge. Unfortunately, his specimen (BSKU 26116, 58.4 mm HL, 300+ mm TL) is in poor condition, but it appears to be a representative of N. tomiyamai . Amaoka et al. (2020) recently listed the species from Hokkaido, but it is obviously based on Sawada’s (1983) record from the Pacific off Tohoku. It should be noted that their photographed specimen represents the holotype collected from “off eastern coast of Japan ” (not from Hokkaido; Okamura 1963a).

Comments on holotype. Nezumia tomiyamai was originally described by Okamura (1963a) based on a single specimen collected from “off eastern coast of Japan ” (no further information). Although he designated the specimen “No. 52045, Zoological Institute, Faculty of Science, Tokyo University” as the holotype of this species, the specimen associated with this catalog number was not found during the author’s visit to the Zoological Museum of the University of Tokyo (ZMUT) in September 2011. However, among the collection was an uncataloged specimen that agrees well with the original description of N. tomiyamai ( Fig. 178 ). This specimen does not bear a catalog number, but it has a cloth tag with the word “higedara” meaning grenadiers (= hige) and gadiform fishes (= dara). A close examination of this specimen along with Okamura’s (1963a) original description has convinced the author that the specimen represents the holotype of N. tomiyamai . No significant differences were found in meristic characters between the ZMUT specimen and the original description ( Table 13 ). Other characters, including dentition, squamation, spinulation of the body scales, and fin position, are also identical between the two. Some differences in morphometric characters, especially in the snout length (27% HL in this study vs. 21% in the original description) and barbel length (15% HL vs. 21%) ( Table 13 ), seem to be attributed to different methods of making measurements. According K. Sakamoto (pers. com., ZMUT), the holotype of N. tomiyamai was probably sent to Okamura prior to registration of the specimen.

Relationships and comparisons. Nezumia tomiyamai is characterized by having 10 or 11 pelvic-fin rays, and falls into “Group E” or “Group F” in the key to species of Nezumia given by Iwamoto (1990), who subdivided the genus into seven groups (A–G) based on the number of pelvic-fin rays. Among species of these two groups, N. tomiyamai is similar to the following three species: N. africana ( Iwamoto, 1970) known from the west coast of Africa; N. atlantica ( Parr, 1946) from the eastern Atlantic; and N. kensmithi Wilson, 2001 from seamounts in the northeastern Pacific. They are closely similar to each other in sharing the following characters: snout short, bluntly pointed, with ventral profile almost vertical; body scales covered with lanceolate or triangular spinules in convergent rows (or densely scattered over exposed portion); underside of snout heavily scaled posterior to lateral angles; and body uniformly dark, lacking prominent dark band encircling trunk.

Nezumia tomiyamai readily differs from these three species in that spinules on the body scales are much smaller, and their rows are more numerous as compared with the latter three species ( Fig. 172 C–D). It is also distinguished by a combination of morphometric characters, including the suborbital width (15–16% HL vs. 12–14%, 12–15%, and 12–14% in N. africana , N. atlantica , and N. kensmithi respectively), preoral length (20–21% HL vs. 15–19%, 10–13%, and 15–21% respectively), internasal width (21–23% HL vs. 18–19%, 15–18%, and 17–20% respectively) and interorbital width (23–25% HL vs. 19–22%, 17–22%, and 19–24% respectively). Nezumia tomiyamai further differs from N. africana in having more pelvic-fin rays (10–11 vs. 8–9), from N. atlantica in having small but prominent pores along the cephalic sensory canals (vs. probably closed, except for the preopercular and postorbital canals), and from N. kensmithi in having fewer scales below the second dorsal-fin origin (8.5 vs. 9–10).

The eastern Pacific N. stelgidolepis ( Gilbert, 1890) and N. pudens Gilbert & Thompson in Thompson, 1916 are similar in general appearance to N. tomiyamai . However, N. stelgidolepis is unlikely to be confused with N. tomiyamai in having prominent scaly patches on lower portions of the branchiostegal membranes (vs. completely naked), and lower counts of transverse scale rows [8–10 vs. 10.5 below the first dorsal-fin origin; 6–7 vs. 7.5–9.5 below the first dorsal-fin midbase; 7–8 (rarely 9) vs. 8.5 below the second dorsal-fin origin]. Nezumia pudens readily differs from N. tomiyamai in that the ventral surface of the snout is completely scaled except for a narrow naked band above the upper jaw (vs. broadly naked). It appears to be further distinguished from N. tomiyamai by having a narrower interorbital space (22– 23% HL vs. 23–25%) and a longer chin barbel (20–25% HL vs. 15–20). [Data for N. stelgidolepis and N. pudens are based on Iwamoto (1979) and this study].

In the original description of N. tomiyamai, Okamura (1963a) considered this species to be most similar to N. burragei ( Gilbert, 1905) , a rare species confined to Hawaii [see also the Comments on Japanese record of Nezumia burragei (given below)]. However, it differs notably from N. burragei in that the mandibular rami are scaled except for anterior portions (vs. completely naked) and the lower surface of the suborbital area is heavily scaled (vs. the underside of the head is broadly naked from the snout tip to a vertical at the posterior margin of the upper jaw (see Gilbert 1905: fig. 260). It further differs from that species in having a wider gill slit (17–18% HL vs. 13%), higher counts of pelvic-fin rays (10–11 vs. 9), and lower counts of scales (longitudinal scales 36–39 vs. 42; scales below the first dorsal-fin origin 10.5 vs. 15.5; below the first dorsal-fin midbase 7.5–9.5 vs. 11; below the second dorsal-fin origin 8.5 vs. 13).

Figures

FIGURE 172. Scanning electron micrographs showing body scales (from the dorsum below the interdorsal space) of two species of Nezumia. (A–B) N. rara sp. nov., NSMT-P 97666, paratype, 71.6 mm HL; (C–D) N. tomiyamai, HUMZ 71963, 68.7 mm HL. (A, C) Views from above; (B, D) oblique views. [Photos: N. Nakayama]

FIGURE 178. Holotype of Lionurus tomiyamai (= Nezumia tomiyamai). ZMUT 52045, 58.4 mm HL, 321+ mm TL, off east coast of Japan, Pacific. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. Preserved condition. [Photos: N. Nakayama]

FIGURE 179. Preserved specimen of Nezumia tomiyamai. HUMZ 71963, 68.7 mm HL, 372+ mm TL, Shichito-Iojima Ridge, Pacific, 580–1100 m depth. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. [Photos: N. Nakayama]