Careproctus rhodomelas Gilbert and Burke, 1912

Murasaki, Kenta, Kai, Yoshiaki, Endo, Hiromitsu & Fukui, Atsushi, 2021, Redescription of the Snailfish Careproctus rhodomelas (Cottoidei: Liparidae), with Ontogenetic and Distributional Notes, Species Diversity 26 (1), pp. 23-29 : 24-28

publication ID	https://doi.org/10.12782/specdiv.26.23
DOI	https://doi.org/10.5281/zenodo.17641398
persistent identifier	https://treatment.plazi.org/id/340A9A0B-FF89-9F1A-1D97-519FD17AFCBB
treatment provided by	Felipe
scientific name	Careproctus rhodomelas Gilbert and Burke, 1912
status

Treatment

Careproctus rhodomelas Gilbert and Burke, 1912 View in CoL

[Standard Japanese name: Bara-bikunin]

( Figs 1–5 View Fig View Fig View Fig View Fig View Fig ; Table 1 View Table 1 )

Careproctus rhodomelas Gilbert and Burke, 1912: 365 , fig. 7, pl. 44 (original description, type locality: off the Bungo Channel, Japan, 741 m depth; paratype locality: south of Suruga Bay , Japan, 927 m depth); Jordan et al. 1913: 307 (off the Bungo Channel and south of Suruga Bay, Japan); Burke 1930: 118, figs 37, 38 (description of the type specimens); Taranetz 1937: 134 (off the Bungo Channel and south of Suruga Bay, Japan; key); Okada and Matsubara 1938: 347 (off the Bungo Channel and south of Suruga Bay , Japan; key); Matsubara 1955: 1194 (off the Bungo Channel and south of Suruga Bay , Japan; key); Okamura 1982: 293, pl. 209 (Bungo Channel to Suruga Bay , Japan; description); Kido 1984: 338, pl. 304-J (Bungo Channel to Suruga Bay , Japan; brief description); Kido 1988: 198, fig. 37 (description of third and fourth specimens from Tosa Bay, Japan, 605–750 m depth); Nakabo 1993: 584, unnumbered fig. (Bungo Channel to Suruga Bay , Japan; key); Nakabo 2000: 669, unnumbered fig. (Bungo Channel to Suruga Bay , Japan; key); Shinohara et al. 2001: 320 ( Tosa Bay , Japan; listed); Chernova et al. 2004: 15 (Bungo Channel to Suruga Bay , Japan; listed); Nakabo and Kai 2013: 1210, unnumbered fig. [?Sea of Japan (off Oki, Shimane); Bungo Channel; Tosa Bay; Suruga Bay , Japan; key].

Materials examined. Holotype: USNM 73334, 111.1 mm SL, male, off the Bungo Channel , Japan, Albatross station 4958 , 32.606°N, 132.408°E, 741 m depth, 23 August 1906. GoogleMaps

Non-types ( 10 specimens, 30.0– 131.4 mm SL): BSKU 20294, 117.8 mm SL, male, off eastern Miyakejima Island, Japan, 34.058°N, 140.000°E, 1160 m depth, 14 November 1972; BSKU 46963, 131.4 mm SL, sex unknown, Tosa Basin (off-shore from Tosa Bay GoogleMaps ), Japan, 32.895°N, 133.678°E– 32.913°N, 133.694°E, 996–1010 m depth, 8 November 1989, R/ V Tansei-maru (KT89-16, T1), beam trawl; BSKU 102864, 87.4 mm SL, male, Hatoma Knoll GoogleMaps , southern Okinawa Trough GoogleMaps , Japan, latitude and longitude unknown, 1530 m depth, 10 May 2005; MSM-20-63, 40.2 mm SL, immature female, South Komagoe Submarine Canyon GoogleMaps , Suruga Bay GoogleMaps , Japan, 34.947°N, 138.550°E– 34.947°N, 138.578°E, 534–821 m depth, 5 February 2008, R/ V Hokuto, epibenthic ring net; MSM-20-64, 30.0 mm SL, immature, off the Fujigawa River GoogleMaps estuary mouth, Suruga Bay GoogleMaps , Japan, 35.060°N, 138.643°E– 35.063°N, 138.683°E, ca. 910 m depth, 16 December 2009, R/ V Hokuto, epibenthic ring net; MSM-20- 65, 75.5 mm SL, male, Hagoromo Submarine Canyon, Suruga Bay, Japan, 35.003°N, 138.553°E– 35.003°N, 138.617°E, 400–1196m depth, 12 December 2012, R/ V Hokuto, beam trawl; MSM-20-66, 52.1 mm SL, immature male, collected with MSM-20-65; MSM-20-67, 35.7 mm SL, immature, collected with MSM-20-65; MSM-20-71, 30.4 mm SL, immature, Hagoromo Submarine Canyon, Suruga Bay GoogleMaps , Japan, 35.005°N, 138.538°E– 35.005°N, 138.617°E, 414–1208 m depth, 16 January 2013, R/ V Hokuto, beam trawl; MSM- 20-72, 30.5 mm SL, immature, Hagoromo Submarine Canyon, Suruga Bay GoogleMaps , Japan, 35.003°N, 138.560°E– 35.005°N, 138.615°E, 460–1209 m depth, 15 March 2013, R/ V Hokuto, beam trawl.

Diagnosis. A species of Careproctus distinguished from all currently recognized congeners by the following combination of characters: total vertebrae 60–63, dorsal-fin rays 54–58, anal-fin rays 48–51, pectoral-fin rays 28–31, teeth on both jaws strongly trilobed, gill slit entirely above pectoral-fin base or extending ventrally to 1st–3rd pectoral-fin ray base, longest ray of lower lobe pectoral fin longer than or nearly equal to HL (90.0–128.0% HL), peritoneum and stomach black.

Description. Counts and measurements given in Table 1 View Table 1 . Body slender, rounded in cross section anteriorly, tapering gradually and becoming moderately compressed posteriorly, deepest at nape region ( Fig. 1 View Fig ). Skin lacking prickles, containing thin subdermal gelatinous layer. Head small, dorsal profile rounded from nape to snout. Snout deep, slightly (or not) projecting. Mouth subterminal, small, oral cleft extending to below center of orbit (or anterior margin of orbit); maxilla extending to below posterior margin of orbit (or between center and posterior margin of orbit) ( Fig. 2A View Fig ). Lower jaw slightly inferior, mandibular tooth plates somewhat behind premaxillary tooth plates. Teeth on both jaws short, strongly trilobed; inner teeth larger than outer teeth ( Fig. 2B View Fig ). Premaxillary teeth in about 10 (6–10) oblique rows of 3–6 (3–9) teeth forming bands. Mandibular teeth in about 9 (5–9) oblique rows of 4–6 (3–8) teeth forming bands. Diastema absent at upper and lower jaw symphyses. Single nostril tube-like, horizontally level with center of orbit. Orbit size moderate, dorsal contour not touching dorsal profile of head; pupil round. Cephalic lateralis pores small, almost same size or smaller than nostril, nasal pores 2, maxillary pores 6, preoperculomandibular pores 7, suprabranchial pores 2; pore pattern 2-6-7-2 (damaged in holotype) ( Fig. 2A View Fig ). Coronal pore absent. Chin pores (=anteriormost preoperculomandibular pores) paired, opening separately, not in common pit. About 13–20 free neuromasts forming irregular rows, originating from around nape and extending posteriorly to about two-thirds of body length (damaged in holotype). Gill slit short, upper margin horizontally level with upper margin of orbit; lower margin entirely above pectoral-fin base or extending ventrally to 1st–3rd pectoralfin ray base (damaged in holotype). Gill rakers restricted to lower part of arch, blunt and minute (status in holotype unknown). Pseudobranch absent (status in holotype unknown). Opercular flap angular (or slightly rounded), supported by two spines; upper spine (from opercle) and lower spine (from subopercle) extending posteriorly to just before vertical through dorsal-fin origin.

Dorsal- and anal-fin rays deeply buried in gelatinous tissue anteriorly. Anteriormost pterygiophore of dorsal fin with ray, inserted between 4th and 5th (or 3rd and 4th) neural spines. Membrane of posterior dorsal-fin rays continuous with caudal fin, overlapping 40.7–51.0% of caudal-fin length (damaged in holotype). Anal-fin origin below 9th (7th–9th) dorsal-fin ray base. Membrane of posterior anal-fin rays continuous with caudal fin, overlapping 43.5–51.0% of caudal-fin length (damaged in holotype). Caudal fin truncate. Hypural plates fused with terminal vertebral centrum, upper and lower plates separated by a narrow slit. A single epural. Two (or three) paired minute pleural ribs on posterior abdominal vertebrae (rarely absent in immature specimens).

Pectoral fin deeply notched, shortest ray at notch shorter than or almost equal to half length of longest ray in both lobes (damaged in holotype). Upper lobe rays slightly free from membrane at tip; 2nd (2nd–4th) ray from dorsalmost longest, reaching to below 7th (6th–9th) dorsal-fin ray base. Lower lobe rays more prominent than upper lobe rays; 5th (3rd–5th) rays from ventralmost longest, longer than (or nearly equal to) head. Rays in notch more widely spaced than on either lobe. Uppermost pectoral-fin base at about 1/2 body depth, lowermost pectoral-fin base below posterior margin of orbit. Proximal radials 4 (3+1), robust, rounded, lacking notches or interradial fenestrae ( Fig. 2C View Fig ). Scapula and coracoid with short stout helve, lacking notches. Distal radials supporting all pectoral-fin rays.

Pelvic disk triangular (rarely slightly oval in immature specimens), longer than wide, anterior lobe well developed and moderately upturned ( Fig. 3 View Fig ). Relative size of pelvic disk widely variable ( Table 1 View Table 1 ), apparently becoming smaller with growth, particularly between 30.0 mm SL and 87.4 mm SL ( Figs 3 View Fig , 4 View Fig ). Anus closer to posterior margin of pelvic disk than to anal-fin origin, vertically below dorsal-fin origin. Small conical urogenital papilla present behind anus (absent in immature specimens). Stomach and pyloric caeca located on left side of visceral cavity.

Color when fresh. Head, body and fin coloration differ with body size: at 75.5 mm SL - anterior part of head (especially snout and chin) reddish, posterior part of head, body, and basal parts of dorsal and anal fins pink, distal margins of dorsal and anal fins dark red, caudal fin reddish, pectoral fin dark red, except black distal margin of upper lobe ( Fig. 1A View Fig ); at 40.2 mm SL - head, anterior half of body, dorsal and anal fins black, posterior half of body, dorsal and anal fins, and caudal fin pale pink, pectoral fin black ( Fig. 1B View Fig ); at 30.0 mm SL - similar to 40.2 mm SL, except pale (whitish) on posterior half of body, dorsal and anal fins, and caudal fin ( Fig. 1C View Fig ). Eye black. Gill cavity and peritoneum (visible through skin) black.

Color in alcohol. Fresh reddish or pinkish colors fading to pale white; black coloration unchanged or becoming slightly lighter. Lips and mouth cavity dusky. Gill cavity, peritoneum and stomach black. Pyloric caeca completely black or mottled at tips.

Distribution. Known from the western North Pacific adjacent to southern Japan: off the eastern part of Miyakejima Island, Suruga Bay, Tosa Bay, off the Bungo Channel, and the Hatoma Knoll (southern Okinawa Trough) in 400– 1530 m depth ( Fig. 5 View Fig ).

Remarks. The newly-collected specimens agreed well with the holotype of C. rhodomelas in having similar counts of vertebrae and fin rays, strongly trilobed teeth, long rays in the pectoral fin lower lobe, and a black peritoneum and stomach. Pelvic disk size and body coloration of examined specimens varied with ontogenetic development. Such changes with development have not been noted previously in species of Careproctus , although Burke (1930) referred to the greatly reduced pelvic disk in the type specimens of C. rhodomelas relative to other species in the genus. They may indicate a life-style change with growth, such as increasing independence from the sea-floor or some substrates. Kobayashi (1962) noted that the pelvic disk of the smooth lumpsucker Aptocyclus ventricosus (Pallas, 1769) belonging to Cyclopteridae [= a sister family of Liparidae (see Orr et al. 2019)] was much smaller in pelagic sub-adult specimens (< 122 mm SL) than in benthic adults ( 160–295 mm SL), and suggested that the size was related to life-style in that species.

Among the species of Careproctus known from the Japanese waters, C. rhodomelas shares trilobed teeth and a dark (brown or black) peritoneum with Careproctus melanurus Gilbert, 1892 , Careproctus simus Gilbert, 1896 , Careproctus marginatus Kido, 1988 , Careproctus rotundifrons Sakurai and Shinohara, 2008 , and Careproctus surugaensis Murasaki, Takami, and Fukui, 2017 ( Stein 1978; Kido 1985, 1988; Sakurai and Shinohara 2008; Murasaki et al. 2017; this study). However, the former clearly differs from the latter species in having 60–63 total vertebrae (vs. 52–55 in C. marginatus , 53–56 in C. rotundifrons and 50 in C. surugaensis ), 54–58 dorsal-fin rays (vs. 47–50 in C. marginatus and C. rotundifrons , and 47 in C. surugaensis ), 48–51 analfin rays (vs. 40–43 in C. marginatus , 41–45 in C. rotundifrons and 39 in C. surugaensis ), 28–31 pectoral-fin rays (vs. 34–40 in C. rotundifrons ), gill slit entirely above pectoral-fin base or extending ventrally to 1st–3rd pectoral-fin ray base (vs. extending ventrally to 7th pectoral-fin ray base in C. surugaensis ), long lower pectoral-fin rays, 90.0–128.0% HL (vs. short, 34.8–50.3% HL in C. simus and 35.8–58.2% HL in C. marginatus ), and a black stomach (vs. pale in all five species) ( Stein 1978; Kido 1985, 1988; Sakurai and Shinohara 2008; Murasaki et al. 2017; this study). In addition, all teeth on both jaws are trilobed in C. rhodomelas (vs. simple teeth mixed in C. simus , C. melanurus and C. rotundifrons ) ( Stein 1978; Kido 1985; Sakurai and Shinohara 2008; Orr et al. 2019; this study).

The voucher-supported records of C. rhodomelas are limited (see Introduction), and other records are uncertain. Yanai (1950) and Kato (1956) listed C. rhodomelas from the Sea of Japan without any voucher specimens or descriptive details, and were later cited by several authors (e.g., Shinohara et al. 2014). However, Yanai (1950) failed to list Careproctus trachysoma Gilbert and Burke, 1912 , despite that species being common in the Sea of Japan, as Nakabo and Kai (2013) pointed out, and may have misidentified C. trachysoma as C. rhodomelas . Accordingly, the record of C. rhodomelas from the Sea of Japan remains unsupported and likely invalid. Takemura et al. (2010) reported reproduction in C. rhodomelas collected by a remotely-operated vehicle (ROV) from around the hydrothermal vents on Hatoma Knoll in the southern part of the Okinawa Trough at 1480–1530 m depth (temperature 3.8–3.9°C). According to their report, the species is a year-round spawner, producing a small number of large elliptic eggs (c.f. usually round in snailfishes) ca. 6 mm in maximum diameter. Sakata et al. (2015) subsequently reported on the visual systems of C. rhodomelas from the Hatoma Knoll by the molecular analysis of rhodopsin, and showed that the eyesight of the specimens appeared sufficiently developed to recognize bioluminescence produced by other animals living near the hydrothermal vents. However, those records of C. rhodomelas from the Hatoma Knoll without showing any supporting evidence for species identification or museum deposition of the specimens for re-examination. The present specimens from off eastern Miyakejima Island (BSKU 20294) and the Hatoma Knoll, southern Okinawa Trough (BSKU 102864) are the first voucher-supported records of C. rhodomelas from those areas, and represent the most eastern, western, and southern records of the species.

Comparative material. Careproctus surugaensis : holotype, MSM-17-81, 82.6 mm SL, female, northern part of Suruga Trough, Suruga Bay, 34.978°N, 138.637°E– 34.923°N, 138.638°E, 1450–1570m depth, 28 October 2015.