Gyrinomimus bruuni Rofen, 1959

Misawa, Ryo, Inuzuka, Atsuki, Fujiwara, Kunihiro, Furusho, Makoto, Tashiro, Fumihito, Takami, Munehiro & Kai, Yoshiaki, 2024, Records of the Rare Flabby Whalefishes Cetomimus hempeli and Gyrinomimus bruuni (Teleostei: Beryciformes) from Japan, Species Diversity 29 (2), pp. 269-279 : 274-277

Gyrinomimus bruuni Rofen, 1959

[New standard Japanese name: Hitaguro-kujirauo] ( Figs 4 , 5 ; Table 2)

Gyrinomimus bruuni Rofen, 1959: 257 , fig. 2 (type locality: off Kenya, southwestern Indian Ocean, 5°25′S, 47°09′E); Paxton 1989: 137 (listed); Rivaton et al. 1990: 33 (listed; New Caledonia); Paxton 1999: 2207 (listed; western central Pacific); Rivaton and Bourret 1999: 304, pl. 143, figs 18, 19 (description of otolith; New Caledonia); Paxton 2000: 602 (listed; South China Sea); Paxton 2002: 1173 (listed; western central Atlantic); Fricke et al. 2011: 372 (listed; New Caledonia); Afonso et al. 2021: 481, fig. 5E (description; 2 spec. from Brazil); Eduardo et al. 2022: 9 (listed; Brazil).

? Gyrinomimus bruuni : Miya et al. 1996: 75 (1 spec. listed from Boso Peninsula , Japan).

Material examined. HUMZ 234625 , 66.2 mm SL, off Ibaraki Prefecture, Japan, 36°31.183′N, 141°21.487′E – 36°31.458′N, 141°21.916′E, 886–892 m depth, bottom temperature 3.3°C, R / V Wakataka-maru, otter-trawl, St . H900, 27 October 2023, coll . K . Fujiwara, S . Tokioka , and M . Furusho.

Description. Counts and measurements (% SL) are as follows: dorsal- and anal-fin rays 20; pectoral-fin rays 16; principal caudal-fin rays 8 + 8 = 16; lateral-line pores 19; branchiostegal rays 10; vomerine tooth rows 3; palatine tooth rows 3; upper jaw tooth rows 3; lower jaw teeth 4; pterygoid tooth rows 2; head length 29.8; snout length 12.6; premaxillary length 24.4; lower jaw length 25.9; premaxilla to opercular margin 5.7; postorbital length 16.5; eye diameter 2.6; eye width 11.4; head width 11.6; premaxillary width 11.0; body depth 18.1; dorsal fin origin to anal fin origin 9.7; caudal peduncle depth 5.7; caudal peduncle length 12.6; snout to pectoral-fin base 30.1; pectoral fin length 10.9; snout to dorsal fin origin 72.6; dorsal-fin base length 18.2; longest dorsal-fin ray 10.4; snout to anal fin origin 72.8; anal-fin base length 16.9; longest anal-fin ray 11.5; anus to 1st anal-fin ray 1.6; copular tooth plate length 9.0; copular tooth plate maximum width 3.1, minimum width 2.1.

Body somewhat elongated, laterally compressed, greatest depth at level of pectoral-fin base, becoming compressed posteriorly; oval in cross section, broadest at top of gill slit ( Fig. 4 ). Dorsal margin of body almost straight. Caudal peduncle length 2.2 times its depth. Anus located just anterior to anal fin origin, distance shorter than eye diameter. Cavernous tissue well developed around anus and along anal-fin base ( Fig. 5A ). Mid-dorsal ridge present from anterior of dorsal fin origin to head. No paired abdominal ridges or diagonal midbody ridges.

Head moderately large, slightly depressed anteriorly, deeper than wide; head and anterior body profile rounded; bony projections prominent on top of head and anterodorsal to eyes. Head broader than body, oval in dorsal view, with moderately rounded snout tip. Nasal organ moderate, with reduced lamella (mostly in anterior nostril). Nostrils paired, round to oval and slightly larger posteriorly, located close together near snout tip, appearance somewhat similar to head lateral-line pores, but slightly deeper than latter. Internasal space rather narrow, distinctly convex. Eye very small, upwardly oval, positioned above approximate mid point of upper jaw. Interorbital space broad, moderately convex, with bony projections.

Mouth enormous, obliquely upward; upper jaw almost straight, lower jaw slightly concave; rictus ca. three times eye diameter before posterior end of premaxilla; posterior end of jaws much closer to opercular margin than level of eye; lower jaw with well-developed lateral spine posteriorly. Jaw teeth short to long, in regular longitudinal rows (three rows in upper jaw, three or four rows in lower jaw), conical with incurved tips, length about 1.0–2.5 times width, those of inner rows longer ( Fig. 5B ). Vomerine teeth moderate to long, in three regular rows, length up to ca. three times width, longer in inner row, tooth patch rather flat, oval ( Fig. 5C ). Palatine teeth moderate to long, in three regular rows, length up to ca. three times width, tooth patch rather short, close to ectopterygoid tooth patch ( Fig. 5C ). Ectopterygoid teeth long, in two regular rows, tooth patch long, slender, beyond level of rictus. Copular teeth rather long, sharp, in irregular rows (ca. 10 rows across narrowest point), tooth patch on single plate, moderately long, slender, length 2.9– 4.1 times width, club-shaped with posterior end largest and rounded, anterior end slightly pointed, midpoint slightly concave.

Three free gill arches with small slit behind ventral arm of third arch; fourth arch strongly reduced and shortened, without following slit; holobranchs well developed on first three arches, relatively tiny on fourth arch ( Fig. 5D, E ). Pseudobranch absent. Gill rakers forming contiguous flat tooth plates ( Fig. 5E ) on first three arches; no tooth plates on medial face of gill arches or ventral pharyngeals.

Lateral line a broad tube pierced by moderate to large circular or oval pores; pores on caudal peduncle without flaps or keels ( Fig. 5F ); lateral-line scales and papillate neuromasts not visible. Head lateral line system with cavernous canals and large pores. Supraorbital canal with about eight pores continuous with main canal (four pores, posteriormost anterior to top of gill slit). Infraorbital canal with eight pores, association with main canal unknown, last pore positioned slightly anterodorsally. Mandibular canal (10 pores) continuous with preopercular canal (four pores). Single, probably isolated pore present just above eye.

Dorsal and anal fins well back on body; anal fin origin under fourth dorsal-fin ray; posterior end of dorsal fin above anal-fin ray 16; length of dorsal- and anal-fin rays almost equal; dorsal and anal fins with 20 rays (probably all simple). Dorsal- and anal-fin bases rather short, dorsal-fin base length 74% of premaxillary length. Anal-fin base with eight lappets (three larger, five smaller). Skin fold along anal-fin base absent; no skin ridges associated with anal-fin rays; no membranous curtain joining posterior anal-fin rays ( Fig. 5A ). Caudal fin partially damaged, short, with 16 principal rays (at least 10 branched). Pectoral fin low, short, directed posteriorly, upper rays longer, with 16 rays (probably all simple). No subpectoral organ visible. Pelvic fin absent.

Coloration. When fresh ( Fig. 4A ) and after preservation ( Fig. 4B ), body entirely jet black.

Distribution. Known from the western Indian Ocean ( Kenya), western Pacific ( New Caledonia, South China Sea, and off Boso Peninsula and Ibaraki Prefecture, Japan), and western Atlantic ( Brazil) ( Rofen 1959; Rivaton et al. 1990; Miya et al. 1996; Paxton 1999, 2000, 2002; Afonso et al. 2021; this study).

Remarks. Five valid species of the genus Gyrinomimus are currently known ( Afonso et al. 2021; Fricke et al. 2024): G. myersi Parr, 1934 , circumglobal; G. bruuni , circumglobal between 30°N and 10°S; G. parri Bigelow, 1961 , western Atlantic, western North Pacific, and western South Pacific; G. grahami Richardson and Garrick, 1964 , cosmopolitan in southern hemisphere; and G. andriashevi Fedorov, Balushkin, and Trunov, 1987 , Antarctic. In addition, an undescribed species (G. sp. sensu Amaoka) has been reported off the Okhotsk coast of Hokkaido, Japan ( Amaoka 1997; Aizawa 2000; Aizawa and Doiuchi 2013). Although the taxonomy of cetomimid species remains confused (e.g., Paxton 1989), with the morphological characteristics of each species poorly documented, the specimen collected off Ibaraki Prefecture, Japan agreed well with the original description of G. bruuni (see Rofen 1959) and additional records from Brazil, western Atlantic ( Afonso et al. 2021), clearly differing from other congeners as follows: 20 dorsal- and anal-fin rays (14–17 in G. myersi , G. parri , G. grahami , and G. andriashevi ); 19 lateral-line pores (15 or 16 in G. myersi and G. parri , 23 in G. andriashevi and G. sp. sensu Amaoka); three and four regular rows of upper and lower jaw teeth, respectively (five or six and 6–8 irregular rows, respectively, in G. myersi , G. andriashevi , and G. sp. sensu Amaoka); three vomerine tooth rows (five in G. andriashevi and G. sp. sensu Amaoka); dorsal-fin base length 18.2% SL (24.0% SL in G. parri , 13.1%–13.8% SL in G. grahami and G. andriashevi ); pectoral fin length 10.9% SL (2.9% in G. andriashevi ); lateral-line flaps absent (present in G. myersi ); and annal lappets present (absent in G. grahami and G. andriashevi ) ( Parr 1934; Rofen 1959; Bigelow 1961; Richardson and Garrick 1964; Fedorov et al. 1987; McEachran and Fechhelm 1998; Paxton 2015; Afonso et al. 2021; Table 1). On the other hand, small differences found between the present study and those of Rofen (1959) and Afonso et al. (2021) included the number of anal-fin rays (20 vs. 18–19) and vomerine tooth rows (3 vs. 2), but the number of specimens available for comparison was small. The differences are currently believed to represent intraspecific variations only.

In addition, a similarity search of the COI gene sequence (639 bp) of the specimen (HUMZ 234625) using the BLAST ® program revealed that more than 98% of the sites matched this sequence only in the specimen identified as Eutaeniophorus sp. (INSDC accession number MN549743; Nonaka et al. 2021). The tapetail larva of Eutaeniophorus Bertelsen and Marshall, 1958 was previously included in the family Mirapinnidae ( Johnson et al. 2009; Nelson et al. 2016; Nonaka et al. 2021). This suggests that Eutaeniophorus sp. (MN549743) is a larva of G. bruuni . On the other hand, only 88.9%–90.3% of the sites matched sequences of G. myersi (NC_012050) and G. grahami (FJ164637, FJ164638, GU80597), indicative of genetic differentiation between G. bruuni and the latter two species.

The first Japanese record of G. bruuni , given without a detailed description, was based on a single specimen (CBM-ZF 460) obtained off the Boso Peninsula, western North Pacific ( Miya et al. 1996). That specimen was loaned to the AMS but is currently missing (M. Miya, personal communication). Therefore, it was not possible to determine here if the two specimens (HUMZ 234625 and CBM-ZF 460) represented the same taxon. Furthermore, the Japanese name “Yase-kujirauo”, proposed by Miya et al. (1996) and subsequently used only by Aizawa and Doiuchi (2013), is here discarded, following the recommendation of the Ichthyological Society of Japan (https://www.fish-isj.jp/iin/standname/ guideline/guidelines2020.pdf). Accordingly, the new standard Japanese name “Hitaguro-kujirauo” is proposed for G. bruuni , based on HUMZ 234625, the first reliable record of G. bruuni from Japan. “Hitaguro” means “uniformly black” in Japanese, in reference to the body color of the specimen. Because the only reliable records of G. bruuni are limited to between 30°N and 20°S ( Paxton 2002), the specimen collected off Ibaraki Prefecture, Japan (36°N) is the northernmost known record of the species. Note that although Aizawa and Doiuchi (2013) considered the specimen reported by Miya et al. (1996) to be from the South China Sea, it was actually from Japanese waters (34°38.04′N, 139°38.03′E, 1150 m depth, R/V Tansei-maru, 7 July 1985; M. Miya, personal communication).

Although Amaoka (1995) proposed the new Japanese name “Hanarabi-kujirauo-zoku” for the genus Gyrinomimus, Aizawa (2000) apparently overlooked that name when proposing “Ooaka-kujirauo-zoku” for the same genus. The latter Japanese name was subsequently used for the genus by Aizawa and Doiuchi (2013), whereas the former name has not been used subsequent to its proposal. Following the recommendation of the Ichthyological Society of Japan, “Ooaka-kujirauo-zoku” should be applied to the genus.

Comparative materials examined. Cetomimus compunctus : ZUMT 55046 (photograph only examined), holotype, 142 mm SL, off Suruga Bay, Shizuoka, Japan, 34°2.8′N, 138°18.8′E, 0–1800 m depth, large plankton net, 19 August 1964. Gyrinomimus sp. sensu Amaoka : HUMZ 121996, 385 mm SL, off Shiretoko Peninsula, Hokkaido, Japan, 44°20′N, 145°7.5′E, 350–460 m depth, gill net, 1980–1992 .

Figures

Fig. 4. Fresh (A) and preserved (B) specimen of Gyrinomimus bruuni, HUMZ 234625, 66.2mm SL, off Ibaraki Prefecture, Japan.

Fig. 5. Close-up photographs of Gyrinomimus bruuni, HUMZ 234625. A, Anus and anal-fin base (right side); B, upper and lower jaw teeth (right side); C, vomerine and palatine tooth patches; D, 3rd and 4th gill arches; E, 1st gill arch; F, lateral-line pores on caudal peduncle (right side). Abbreviations:AL, anal lappets; AN, anus; CT, cavernous tissue; GA1, 3 and 4, 1st, 3rd and 4th gill arches, respectively; LLP, lateral-line pores; PAL, palatine tooth patch; V, vomerine tooth patch. Scale bars, 3mm.