Cetomimus hempeli Maul, 1969

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 : 270-274

publication ID	https://doi.org/10.12782/specdiv.29.269
persistent identifier	https://treatment.plazi.org/id/A6476644-6B34-DA6A-F1D3-D822FB19FD9B
treatment provided by	Felipe
scientific name	Cetomimus hempeli Maul, 1969
status

Treatment

Cetomimus hempeli Maul, 1969 View in CoL

[New standard Japanese name: Seiun-kujirauo] ( Figs 1–3 View Fig View Fig View Fig ; Table 1)

Cetomimus hempeli Maul, 1969: 3 View in CoL , fig. 1 (type locality: eastern Atlantic, 27°50′N, 14°01′W); Paxton 1989: 137 (listed); Tolley et al. 1989: 673 (brief description; 4 spec. from Gulf of Mexico); McEachran and Fechhelm 1998: 987 [key; description after Maul (1969) and Tolley et al. (1989); Gulf of Mexico]; Carneiro et al. 2014: 43 View Cited Treatment (listed; Portugal); Paxton et al. 2016: 2178 (key; brief description; eastern central Atlantic); Carneiro et al. 2019: 154 (listed; Portugal).

Material examined. FAKU 149611 View Materials , 89.5 mm SL, female, off Fukushima Prefecture, Japan, 36°50.594′N, 141°41.608′E – 36°50.934′N, 141°41.937′E, 902–903 m depth, bottom temperature 3.1°C, R / V Wakataka-maru, otter-trawl, St GoogleMaps . G900, 11 November 2022, coll . E GoogleMaps . Morikawa , R . Misawa , and J . Nagao ; MSM-24-6, 48.5 mm SL, female, off the Kii Peninsula, Japan, 32°04.892′N, 136°51.597′E – 32°05.241′N, 137°00.332′E, wire out 5000 m, RT/ V Bosei-maru, IKMT, mesh size 0.53 mm, 29 September 2013 GoogleMaps .

Description. Counts and measurements (% SL) are as follows: dorsal-fin rays 17; anal-fin rays 16–17; pectoral-fin rays 23–24; principal caudal-fin rays 8 + 8–9 = 16–17; lateral-line pores ca. 20–23; vertebrae 33 + 15 = 48 (including urostyle); branchiostegal rays 10; vomerine tooth rows 6–8; palatine tooth rows 4; upper jaw tooth rows 5; lower jaw tooth rows 5–6; pterygoid tooth rows 6; head length 30.5– 32.9; snout length 11.3; premaxillary (upper jaw) length 26.2–28.4; lower jaw length 28.5–29.8; premaxilla to opercular margin 5.2–6.8; postorbital length 16.7–18.6; eye diameter 1.6–2.0; eye width 14.0–14.8; head width 12.0–16.5; premaxillary width 16.5–16.8; body depth 17.7–20.4; dorsal fin origin to anal fin origin 11.5–17.7; caudal peduncle depth 6.0–6.9; caudal peduncle length 8.7–11.4; snout to pectoral-fin base 30.1–33.9; pectoral fin length 8.0–8.8; snout to dorsal fin origin 71.1–74.4; dorsal-fin base length 13.0–16.1; longest dorsal-fin ray 8.2–8.5; snout to anal fin origin 70.9– 76.2; anal-fin base length 13.0–13.8; longest anal-fin ray 8.3–9.0; anus to 1st anal-fin ray 1.9–2.7; copular tooth plate length 5.6–7.4; copular tooth plate maximum width 2.3–2.6, minimum width 1.4–1.5.

Body tadpole-like, greatest depth at level of pectoral-fin base, becoming compressed posteriorly; oval in cross section, broadest at top of gill slit ( Fig. 1 View Fig ). Dorsal margin of body moderately curved. Caudal peduncle length 1.5–1.6 times its depth. Anus located just anterior to anal fin origin, distance slightly longer than eye diameter. Cavernous tissue well developed around anus and from anal fin origin to first 3–4 rays, weakly developed from dorsal fin origin to first 3–4 rays ( Figs 2A, B View Fig , 3 View Fig ). Mid-dorsal ridge present from anterior of dorsal fin origin to head, gradually becoming higher anteriorly. No paired abdominal ridges or diagonal midbody ridges.

Head very large, slightly depressed anteriorly, deeper than wide; head and anterior body profile weakly rounded; bony projections prominent on top of head and postero- and anterodorsal to eyes. Head broader than body, oval in dorsal view, with rounded snout tip. Nasal organ moderate with reduced lamella, mostly in anterior nostril. A pair of nostrils close together, slightly larger posteriorly, round to oval, located near snout tip, somewhat similar to but larger than head lateral-line pores. Internasal space broad, rather convex. Eye very small, slightly upwardly elongated, situated near snout tip. Interorbital space broad, distinctly 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 moderately developed lateral and ventral spines posteriorly. Jaw teeth small, conical, length ca. 1.0– 1.5 times width, slightly longer in inner rows ( Fig. 2C View Fig ); teeth in almost regular diagonal rows, upper jaw with five anterior and three posterior rows, lower jaw with 5–6 anterior and 3–4 posterior rows. Vomerine teeth short, blunt, with 6–8 rows, tooth patch domed, round ( Fig. 2D View Fig ). Palatine teeth short, with four (two anterior, three posterior) rows, tooth patch rather short, slightly separated from ectopterygoid tooth patch ( Fig. 2D View Fig ). Ectopterygoid teeth short, with six (2–3 anterior) rows, tooth patch long, slender, beyond level of rictus. Copular teeth short, blunt, in irregular rows, about 7–9 rows across narrowest point; tooth patch on single plate, moderately long, slender, length 2.4–4.9 times width, club-shaped with posterior end largest and rounded, anterior end moderately pointed, with narrow midpoint.

Three free gill arches with small slit behind ventral arm of third arch; fourth arch strongly reduced, shortened, without posterior slit; holobranchs well developed on first three arches, tiny on fourth arch ( Fig. 2E, F View Fig ). Pseudobranch absent. Gill rakers forming contiguous flat tooth plates ( Fig. 2F View Fig ) 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 pores, those on caudal peduncle circular or oval, with small triangular flaps ( Fig. 2G View Fig ); lateral-line scales not visible; one or two papillate neuromasts on some remaining skin bridges, especially prominent on caudal peduncle. Lateral-line system of head with cavernous canals with moderate to large pores. Supraorbital canal with about eight pores, joined to main canal (with three pores, posteriormost anterior to top of gill slit). Infraorbital canal with seven pores (association with main canal unknown), posteriormost pore positioned slightly anterodorsally. Mandibular canal with nine pores, probably continuous with preopercular canal (six pores). Two apparently isolated pores posterodorsal to eye.

Dorsal and anal fins well back on body; anal fin origin under second dorsal-fin ray; ends of dorsal and anal fins opposite; posterior dorsal- and anal-fin rays longer; dorsal fin with 17 rays, 9–10 simple, 6–7 branched and one simple; anal fin with 16–17 rays, 7–8 simple, eight branched and one simple. Dorsal- and anal-fin bases short, dorsal-fin base length 50%–57% of premaxillary length. No anal lappets with internal scales; skin fold along anal-fin base absent; skin ridges present, associated with 1–13 anal-fin rays; no membranous curtain joining posterior anal-fin rays ( Fig. 2A View Fig ). Caudal fin partially damaged, but short, weakly rounded, middle rays longest, with 16–17 principal rays (3 simple + 10 branched + 3–4 simple). Pectoral fin low, short, directed posteriorly, upper rays longer, with 23–24 simple rays. No subpectoral organ visible. Pelvic fin absent.

Ovaries paired, orangish, protruding from ruptured abdomen; egg diameter ca. 0.10–0.15 mm.

Coloration. When fresh ( Fig. 1A View Fig ), body largely brownish-black mixed with reddish-orange; skin bridges of lateral line jet black; head more strongly reddish; dorsal- and pectoral-fin rays largely grayish; anal-, caudal-, and posterior dorsal-fin rays bright reddish-orange. After preservation ( Fig. 1B, C View Fig ), reddish color faded, becoming mostly dark to charcoal brown; all fin tips pale gray.

Distribution. Known from the eastern Atlantic (Canary Islands, Madeira, and west coast of Africa), western Atlantic (Gulf of Mexico), and western North Pacific (off Fukushima Prefecture and Kii Peninsula, Japan) ( Maul 1969; Tolley et al. 1989; Paxton et al. 2016; this study).

Remarks. Eight valid species of the genus Cetomimus are currently known ( Kobyliansky et al. 2023; Fricke et al. 2024): C. gillii Goode and Bean, 1895 , circumglobal; C. pick-

Abbreviations: D, dorsal-fin rays; A, anal-fin rays; P1, pectoral-fin rays; LLP, lateral-line pores; CT, cavernous tissue; DB, dorsal-fin base length; PmL, premaxillary (upper jaw) length.

Numerals in parentheses indicate number of individuals.

lei (Gilchrist, 1922), southeastern Atlantic; C. kerdops Parr, 1934 , Bahamas; C. craneae Harry, 1952 , western Atlantic; C. teevani Harry, 1952 , western Atlantic; C. compunctus Abe, Maruno, and Kawaguchi, 1965 , western North Pacific and western South Atlantic; C. hempeli , Atlantic Ocean and probably North Pacific; and C. paxtoni Kobyliansky, Gordeeva, and Mishin, 2023 , central Atlantic. The specimens described herein, collected off Fukushima Prefecture and Kii Peninsula, Japan, agreed strongly with the original description of C. hempeli ( Maul 1969) and additional records of that species from the Gulf of Mexico ( Tolley et al. 1989), clearly differing from other congeners by the following characters: head rounded in dorsal view and distinctly broader than the body (head sharply pointed, as broad as the body in C. kerdops ); reduced fourth gill arch and slit between third and fourth arches (fourth gill arch completely reduced and no slit behind third arch in C. gillii , C. craneae , and C. teevani ); cavernous tissue present around dorsal fin origin and absent from caudal peduncle (absent from dorsal fin origin in C. gillii , C. picklei , and C. paxtoni , and present above and below caudal peduncle in C. compunctus ; posterior lateral-line pores with small flaps (with large flaps in C. craneae and C. teevani ); and dorsal-fin base length apparently shorter than upper jaw length (slightly longer in C. compunctus ) ( Goode and Bean 1895; Brauer 1906; Parr 1934; Harry 1952; Abe et al. 1965; Paxton and Bray 1986; McEachran and Fechhelm 1998; Angulo 2015; Paxton et al. 2016; Kobyliansky et al. 2023; Table 1). On the other hand, a small difference was found between the present study and those of Maul (1969) and Tolley et al. (1989) in the number of pectoral-fin rays (23–24 vs. 17–23), but the number of specimens available for comparison was small. The difference is currently believed to represent intraspecific variation only.

In addition, a similarity search of the COI gene sequence (588 bp) of the specimen (FAKU 149611) using the BLAST ® program revealed that more than 98% of the sites matched this sequence only in the specimen identified as Ataxolepis apus Myers and Freihofer, 1966 (INSDC accession number ON810779; Kobyliansky et al. 2023). The bignose fish male of Ataxolepis Myers and Freihofer, 1966 was previously included in the family Megalomycteridae ( Johnson et al. 2009; Nelson et al. 2016). This suggests that the male specimen of A. apus (ON810779) is a male of C. hempeli . On the other hand, only 96.3%–96.5% of the sites matched the sequences of C. paxtoni (ON810776, ON810777; Kobyliansky et al. 2023), indicative of genetic differentiation between C. hempeli and C. paxtoni .

Approximately 10 specimens of C. hempeli have been recorded from the Atlantic Ocean ( Maul 1969; Tolley et al. 1989; Paxton et al. 2016), and although Paxton et al. (2016) suggested that the species may also occur in the North Pacific, no reliable records of such existed at that time. Therefore, the present specimens represent the first reliable records from the Pacific Ocean, and the specimen collected off the Fukushima Prefecture coast (FAKU 149611) is the northernmost record of the species [previous northernmost record, Funchal, Madeira, Portugal ( Maul 1969)]. The new Japanese name “Seiun-kujirauo” is proposed for C. hempeli based on FAKU 149611. “Seiun” means “nebula” in Japanese and refers to the nebula-like cavernous tissue of the anal- and dorsal-fin origins, while “kujirauo” being the common Japanese name for flabby whalefishes.

Paxton (1989) noted that “the cavernous tissue appears more sharply defined and more clearly organized in small- er specimens of all taxa”. In fact, the cavernous tissue was relatively indistinct in the larger specimen (FAKU 149611, 89.5 mm SL; Fig. 2A, B View Fig ), but more distinct in the smaller specimen (MSM-24-6, 48.5 mm SL; Fig. 3 View Fig ).