Nezumia rara, Nakayama, Naohide, 2020

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 256-261

Nezumia rara sp. nov.

[New Japanese name: Kakure-hige]

( Figs. 171 , 172 A–B; Table 13 ; Appendix 3-10D)

[?] Macrourus burragei (not Gilbert 1905): Kamohara 1937:189, fig. 2 (first record from Japan; brief description; 1 spec. from Kochi; new Japanese name: “Nan’yo-dara”); Kamohara 1938:72, fig. 41 [after Kamohara (1937)].

[?] Lionurus burragei (not Gilbert 1905): Okada & Matsubara 1938:453 (in key; Japan); Kamohara 1950:278 (listed; Kochi Pref.); Kamohara 1952:98, fig. 96 [brief description after Kamohara (1937); Kochi Pref.]; Matsubara 1955:1316 (in key; Japan); Kamohara 1958:74 (questionable; listed; Kochi Pref.); Kamohara 1964:96 (questionable; listed; Kochi Pref.).

[?] Nezumia burragei (not Gilbert 1905): Okamura 1970a:100 [description after Gilbert (1905) and Kamohara (1937, 1938)]; Okamura 1970b: table 1 (listed; Japan); Tominaga & Uyeno 1981:489 (listed; Japan); Okamura 1984b:94, pl. 345, fig. C (compiled); Okamura 1988:94, pl. 345, fig. C (compiled); Nakabo 1993:360 (in key; Japan); Nakabo 2000:424 (in key; Japan); Shinohara et al. 2001:306 (listed; Tosa Bay); Nakabo 2002:424 (in key; Japan); Nakabo & Kai 2013:500 (in key; Japan); Motomura 2020:39 (listed; Japan).

Nezumia sp.: Sawada 1983:107, 193, fig. 59 (brief description; 1 spec. from Pacific off Tohoku; HUMZ 78437 ) .

Diagnosis. A species of Nezumia with 10–11 pelvic-fin rays. Snout short, protruding scarcely beyond upper jaw, length 26–28% HL, ventral contour almost vertical in lateral view; underside of snout broadly naked; ventral surfaces of head scaled posterior to lateral angles of snout; mandibular rami mostly scaled; orbit–preopercle distance 39–41% HL; interorbital width 20–22% HL; pelvicfin length 46–54% HL; length of outer gill slit 13–16% HL. Second spinous ray of first dorsal fin not extremely prolonged(height of fin 80–98% 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 dorsalfin origin 9–10. Cephalic sensory pores present along all canals, but barely discernible. No prominent dark band encircling trunk; first dorsal fin uniformly dark.

Material examined. 3 specimens. Holotype: NSMT-P 100179 (73.0 mm HL, 419 mm TL), Suruga Bay , Shizuoka Pref., Japan, R/ V Tansei-maru, cr. KT-78- 19, sta. TW5, 2-m beam trawl, Dec. 1978 . Paratypes: NSMT-P 97666 (1, 71.6 mm HL, 415 mm TL), southeast of Oshima Island , Shichito-Iojima Ridge, 621–710 m, R/ V Hakuho-maru, cr. KH-89-test-III, 4-m beam trawl, 5 Sept. 1989; HUMZ 78437 (1, 78.9 mm HL, 447+ mm TL) , off Ibaraki, 36.0583ºN, 141.3333ºE, 1100 m, bottom trawl, coll. K. Sakamoto, 9 Jan. 1978 .

Description. General features are shown in Fig. 171 . Counts and measurements are given in Table 13 . The following description based on the holotype, unless otherwise stated; variations found in paratypes are indicated in parentheses. Body moderately deep, deepest at first dorsal-fin origin, gradually tapering to long, slender tail. Trunk short, compressed, width over pectoral-fin bases 1.5 in depth below first dorsal-fin origin. Head moderately large, HL about 5.7 (5.7–5.8) in TL; dorsal profile almost straight from tip of snout to first dorsal-fin origin, without pronounced hump over nape nor distinct depression above orbits. Snout short, protruding scarcely beyond upper jaw, ventral contour almost vertical, forming angle of about 70º to horizontal axis of head and body; snout length 0.9 (0.9– 1.1) times as long as orbit diameter; tip of snout situated above horizontal through midorbit, bluntly pointed in lateral and dorsal views. Orbit moderately large, circular in outline, greatest diameter 1.6 (1.7–1.9) in postorbital length. Interorbital space almost flat (slightly concave), width 1.4 (1.2–1.4) in orbit diameter. Mouth moderately small, subinferior, upper-jaw length 0.8 in orbit diameter; posterior margin of maxilla extending to vertical through hind 1.3 of orbit (midorbit); lateral corner of mouth slightly restricted by lip folds; lips thick, fleshy, papillose near tooth bands. Suborbital region narrow, divided into upper and lower halves by infraorbital ridge. Preopercle large, hind margin slightly inclined forward, forming broad lobe posteroventrally; preopercular ridge low, with slight backward extension at posteroventral corner. Interopercle narrowly exposed beyond preopercle. Gill membranes broadly connected across, and attached mesially to isthmus, with broad posterior free fold. Anteroventral end of gill opening not reaching below posterior margin of lower jaw. Outermost gill slit moderately restricted by skin folds, length 1.8 (2.0) in orbit diameter. Gill rakers developed into small, ridge-like tubercles, their tips armed with short, fine spines; rakers on outer side of first arch and inner side of fourth arch much smaller than others. Gill filaments moderately long. Barbel long, slender, filamentous at tip, length 1.7 (1.3) in orbit diameter.

Anus closer to pelvic-fin bases than to anal-fin origin. Periproct broad, teardrop-shaped. Anterior dermal window of light organ small, circular, situated between inner bases of pelvic fins.

Teeth short, slender, conical, in tapered bands in both jaws. Premaxillary teeth arranged in about 5–6 tooth rows near symphysis, with outermost series distinctly enlarged. Mandibular band with about 5 tooth rows at widest point near symphysis, and no teeth significantly enlarged. Posterior ends of tooth bands falling short of lateral corner of mouth in both jaws. All teeth deeply embedded in thick layer of gum papillae.

Body scales small, thin, not especially deciduous, covered with short, greatly reclined, narrowly triangular spinules in tightly packed convergent rows or densely scattered over exposed portion ( Fig. 172 A–B); tip of last spinule in each row extending slightly beyond posterior scale margin; middle row of spinules not enlarged; buttresses of spinules absent; reticulate structure narrowly developed on posterior parts of unexposed portion. Body fully scaled except for fins, periproct, and dermal window of light organ; proximal portion of pelvic fins heavily covered with tiny scales.

Suborbital shelf armed with stout, coarsely modified scales. Snout tipped with 2 enlarged, thickened, closely adjoined tubercles; scales on lateral angles of snout modified into scute-like scales. Other scales on head covered with short, erect, triangular spinules in parallel to divergent rows. Dorsal and lateral surfaces of head almost fully scaled; membrane around anterior nostril and paired Y-shaped areas dorsally posterior to leading edges of snout narrowly naked. Underside of snout almost completely naked; lower half of suborbital region mostly scaled, but narrowly naked above upper lip; anterior 1/3 of mandibular rami naked; gular and branchiostegal membranes lacking scales.

Cephalic sensory pores present along sensory canals; those on underside of head very slightly enlarged, more or less tubular. Free neuromasts densely scattered over naked areas on underside of snout and mandibular rami, and serially arranged along leading edges of snout, supranarial ridges, suborbital shelf, and supraorbital canals; those on underside of snout largest. Naked area on underside of snout densely covered with short, hairlike papillae. Grooved lateral line incomplete anteriorly, occurring as short interrupted segments, but complete posterior to vertical through midbase of first dorsal fin.

Origin of first dorsal fin slightly posterior to vertical through pectoral-fin base; first dorsal fin high, its height 3.4 (2.7–3.0) times as long as its base length; second spinous ray long, but not especially elongate, armed along its leading edge with short, reclined, conical, narrowly spaced denticles; its tip extending to base of 11th (8th) second dorsal-fin ray when laid back. Second dorsal fin well separated from first dorsal, originating above 10th (9th–10th) anal-fin ray; interdorsal space 1.4 times as long as first dorsal-fin base length. Pelvic fin inserted below pectoral-fin base; outermost ray moderately elongate with filamentous tip, reaching base of 4th (3rd) anal-fin ray when laid back.

Color when fresh. Unknown.

Color in alcohol ( Fig. 171 ). Head and body uniformly dark overall, with much darker abdomen; orbit barely marked with narrow dark rim; lips broadly delineated in dark brown; septum between nostrils much darker than surroundings; oral cavity blackish including gum papillae; gill cavity mostly black, but paler on ceratohyal, epihyal, and anterior to lower end of cleithrum; gill rakers and arches pale to dusky, filaments orange brown; chin barbel mostly pale with dusky base; gular membrane blackish; fins uniformly dark, but outermost pelvic-fin ray paler.

Size. To about 45 cm TL ( HUMZ 78437 , 447 + mm TL, off Ibaraki Pref., Japan) .

Distribution. So far known only from Japan: Suruga Bay, off the Izu Islands, and Kashima-nada, at depths of 621‾1100 (Appendix 3-10D). Very rare.

Etymology. The specific epithet is derived from the Latin adjective rarus, meaning “sparsely occurring”, in reference to the species’ rare occurrence. The Japanese name, Kakure-hige, also alludes to the rarity of the species (kakure, meaning “hiding”, and hige, meaning “ grenadiers ”.

Remarks. Sawada (1983) reported “ Nezumia sp.” based on a single specimen collected from off Ibaraki, Japan (HUMZ 78437, 78.9 mm HL, 477+ mm TL). His specimen is herein designated as a paratype of the new species. See also the Comments on the Japanese record of Nezumia burragei (given below).

Relationships and comparisons. Nezumia rara sp. nov. is very similar to N. tomiyamai (Okamura, 1963) , with which it shares most of the diagnostic features separating the latter species from its congeners. No differences were found in meristic characters, except for transvers scale rows below the second dorsal-fin origin (9–10 in N. rara vs. 8.5 in N. tomiyamai ; Table 13 ). However, regarding morphometric characters, the two species are different in many aspects, including the postorbital length (46–49% HL in N. rara vs. 49–51% in N. tomiyamai ), postrostral length (74–75% vs. 77%), orbit–preopercle distance (39–41% vs. 42–43%), upperjaw length (33–36% vs. 36–37%), interorbital width (20– 22% vs. 23–25%), pelvic-fin length (46–54% vs. 69%), pectoral-fin length (61–63% vs. 58%), and length of gill slit (13–16% vs. 17–18%) ( Table 13 ). These differences are subtle, but in combination, they appear to warrant their specific separation. In fact, the general appearance of the two species is quite different from each other ( Fig. 171 vs. Figs. 178–179 ), which results from the differences in the above-mentioned characters.

TABLE 13. (Continued)

Nezumia shinoharai Nakayama & Endo, 2012 [Japanese name: Shinohara-hige]

( Figs. 173–174 , 175A ; Appendix 3-10E)

Nezumia shinoharai Nakayama & Endo, 2012:62 , figs. 1–3, 4A. (original description; holotype: NSMT-P 97667, from Pacific off Boso Peninsula, in 627–673 m; 1 paratype from Tosa Bay; new Japanese name: “Shinohara-hige”); Nakabo & Kai 2013:1874 (comments on Japanese records); Motomura 2020:39 (listed; Japan).

Diagnosis. A species of Nezumia with 10 pelvic-fin rays. Snout moderately long, conical, protruding well beyond upper jaw, length 31–34% HL, ventral contour oblique in lateral view; underside of head almost completely naked. Second spinous ray of first dorsal fin not extremely prolonged (height of fin 99% HL). Body scales covered with short, greatly reclined, needle-like spinules in discrete parallel rows; tip of last spinule in each row extending well beyond posterior scale margin; middle row of spinules not enlarged; scales below second dorsal-fin origin 8–9. Cephalic sensory pores well developed especially on mandibular and infraorbital canals. No prominent dark band encircling trunk; first dorsal fin uniformly dark with pale tip.

Material examined. 2 specimens. Holotype of Nezumia shinoharai : NSMT-P 97667 (38.0 mm HL, 244+ mm TL), east of Boso Peninsula , Chiba Pref., Japan, 35.1048ºN, 140.8367ºE, 627–673 m, R/ V Tansei-maru, cr. KT-95-05, sta. TB16, 3-m ORE beam trawl, 25 Apr. 1995 . Paratype of N. shinoharai: BSKU 44790 (1, 33.3 mm HL, 198+ mm TL), Tosa Bay , 33.0517ºN, 133.6152ºE, 700 m, FRV Kotaka-maru, 24 May 1988 .

Counts and measurements. Based on 2 specimens (33.3–38 mm HL, 198+–244+ mm TL). Counts: first dorsal-fin rays II,9; pectoral-fin rays i20–i24; pelvic-fin rays 10; gill rakers on first arch (outer/inner) 9/10–11, on second arch 10/10–11; longitudinal scales 38–39; transverse scale rows below first dorsal-fin origin 10.5, below first dorsal-fin midbase 7.5, below second dorsalfin origin 8–9.

The following measurements are in % of HL, followed by those in % of PRL in parentheses: snout length 31–34 (45–49); orbit diameter 29–30 (43–43); postorbital length 39–42 (57–60); postrostral length 68–69; orbitpreopercle distance 34–35 (50); suborbital width 14–15 (21–22); upper-jaw length 26–27 (38–40); length of rictus 19–20 (28–29); length of premaxillary tooth band 14 (20); preoral length 29–30 (42–44); distance between tip and lateral angle of snout 18–19 (27); snout width 25– 26 (36–37); internasal width 22–22 (32–32); interorbital width 23–25 (33–36); body width over pectoral-fin bases 42–47 (61–68); body depth at first dorsal-fin origin 71–80 (104–116); body depth at anal-fin origin 66 (96); prepelvic length 102–105 (147–154); preanus length 113–120 (163–175); preanal length 134–142 (193–208); isthmuspelvic distance 35–36 (51–52); pelvic–anal distance 37– 41 (53–61); anus–anal distance 23–24 (33–34); pelvic-fin length 62–65 (90–96); pectoral-fin length 52–55 (77–79); predorsal length 113–116 (166–167); height of first dorsal fin 99 (143); length of first dorsal-fin base 23–28 (34–40); interdorsal length 39–41 (58–59); length of gill slit 12–14 (17–20); length of posterior nostril 8 (11); barbel length 11–12 (15–17).

Size. To about 24 cm TL ( NSMT-P 97667 , holotype, 244+ mm TL, east of Boso Peninsula , Japan) .

Distribution. So far known only from off the Boso Peninsula and Tosa Bay at depths of 627–700 m ( Nakayama & Endo 2012; Appendix 3-10E). Very rare.

Remarks, relationships, and comparisons. Nezumia shinoharai was recently described by Nakayama & Endo (2012) based on two specimens collected from southern Japan ( Figs. 173–174 ). Apart from the type specimens, no additional materials are available for this study. It belongs to the N. spinosa group as defined by Nakayama & Endo (2015), in which the following six species are included: N. aspidentata Iwamoto &Merrett, 1997 from New Caledonia; N. holocentra ( Gilbert & Cramer, 1897) from Hawaii; N. infranudis Gilbert & Hubbs, 1920 from the Celebes and Timor Seas; N. merretti Iwamoto & Williams, 1999 from the eastern Indian Ocean; N. shinoharai ; and N. spinosa ( Gilbert & Hubbs, 1916) from the Indo-West Pacific.

Nezumia shinoharai readily differs from other species of that group by its unique spinulation on the body scales: in N. shinoharai , spinules are arranged in discrete parallel rows ( Fig. 175A ), whereas those of the other five species are in tightly packed subparallel or convergent rows, or densely scattered over the exposed portion of the scales. It also differs from all but N. aspidentata in having 10 pelvic-fin rays (vs. 8–9 or 11). For further details see Nakayama & Endo (2012, 2015).

Figures

FIGURE 171. Holotype of Nezumia rara sp. nov. NSMT-P 100179, 73.0 mm HL, 419 mm TL, Suruga Bay, Shizuoka Pref., Pacific. (A) Lateral, (B) dorsal, and (C) ventral views. Preserved condition. [Photos: N. Nakayama]

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 173. Fresh specimen of Nezumia shinoharai. BSKU 44790, paratype, 33.3 mm HL, 198+ mm TL, Tosa Bay, Kochi Pref., Pacific, 700 m depth. Lateral view. [Photo: reproduced from Nakayama & Endo (2012: fig. 2A)]

FIGURE 174. Holotype of Nezumia shinoharai. NSMT-P 97667, 38.0 mm HL, 244+ mm TL, east of Boso Peninsula, Chiba Pref., Pacific, 627–673 m depth. (A) Lateral view; (B) dorsal and (C) ventral views of head. Preserved condition. [Photos: (A) reproduced from Nakayama & Endo (2012: fig. 1); (B–C) N. Nakayama]

FIGURE 175. Scanning electron micrographs showing body scales (from the dorsum below the interdorsal space) of two species of the Nezumia spinosa group. (A) N. shinoharai, NSMT-P 97667, holotype, 38.0 mm HL; (B) N. spinosa, USNM 76868, holotype, 46.4 mm HL. Views from above. [Photos: reproduced from Nakayama & Endo (2012: fig. 4A, E)]

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]