The genus Careproctus Krøyer 1862 is one of the most diverse genera in the family Liparidae, comprising over 130 species distributed worldwide, except in the Indian Ocean (Chernova et al. 2004; Fricke et al. 2022). Although a recent molecular phylogenetic study has demonstrated that the genus is paraphyletic (see Orr et al. 2019), Careproctus sensu lato is primarily recognizable by the following morphological characters: a single nostril on each side; pseudobranch absent; pelvic disk present; pectoral fins typically with fewer rays than anal fin; and body color uniformly light or dark, often gradually darkening posteriorly when otherwise light, rarely variegated (Orr and Maslenikov 2007). Although the genus Osteodiscus Stein 1978 shares most of these characters, it differs from Careproctus in having a skeletal pelvic disk without a fleshly margin, and no pleural ribs on the posterior abdominal vertebrae (Murasaki et al. 2021a). Each species of Careproctus has been distinguished traditionally by vertebral and fin ray counts, teeth and pectoral-fin shapes, pelvic disk shape and size, and peritoneal coloration, among other characters (see Gilbert and Burke 1912a, b; Burke 1930; Schmidt 1950; Stein 1978; Kido 1988; Andriashev and Stein 1998; Chernova 2005; Kai et al. 2011; Murasaki et al. 2017; Orr et al. 2020). Additionally, the structure of the pectoral girdle has been used as an important diagnostic character for identifying snailfishes, including species of Careproctus, since the study of Andriashev et al. (1977).

Thirty-three species of Careproctus have been described or listed from Japanese waters to date, many of them from the Sea of Japan, Sea of Okhotsk, and Pacific coast of northern Japan (north of Boso Peninsula, Chiba) (Kai et al. 2011, 2018, 2019, 2021; Machi et al. 2012; Nakabo and Kai 2013; Orr et al. 2015, 2020; Murasaki et al. 2017; Kai and Matsuzaki 2019; Matsuzaki et al. 2020). Conversely, only three species are currently known from the Pacific coast of southern Japan: Careproctus rhodomelas Gilbert and Burke 1912a, Careproctus rotundifrons Sakurai and Shinohara 2008, and Careproctus surugaensis Murasaki, Takami and Fukui 2017 (Sakurai and Shinohara 2008; Murasaki et al. 2017, 2021b). During a recent survey of deep-sea fauna conducted by the Marine Science Museum, Tokai University, Shizuoka, Japan (MSM), an unidentified example of Careproctus was captured by bait trap from Suruga Bay, southern Japan (Fig. 1). It was later found to be conspecific with three specimens collected previously from Tosa Bay and the Hyuga-nada Sea, and deposited in the fish collections of the Faculty of Science and Technology, Kochi University, Kochi, Japan (BSKU). Because these four specimens were clearly distinguishable from all congeners, they are described herein as a new species.

Fig. 1
figure 1

Collection localities of Careproctus tomiyamai sp. nov.

Materials and methods

Counts, measurements, and descriptive terminology follow Andriashev and Stein (1998), with the exceptions of cephalic pore terminology, which follows Stein et al. (2001), and osteological terminology for the pectoral girdle, which follows Orr and Maslenikov (2007). Counts of vertebrae, their accessory bones, and median-fin rays were made from radiographs. Counts of gill rakers were taken from the first gill arch on the right or left sides of all paratypes. Cephalic pores were examined after staining with Aniline Blue. Pectoral girdles were removed from two paratypes (left side in BSKU 44396, right side in BSKU 48172), and stained with Alizarin Red (BSKU 44396), and Alcian Blue and Alizarin Red (BSKU 48172). The statuses including counts and measurements are presented in species accounts as the range for all material examined followed by the value for the holotype in parentheses when intraspecific variation is indicated. Standard length and head length are abbreviated as SL and HL, respectively. The specimens examined (including comparative material) are deposited in BSKU, MSM, the fish collections of Kyoto University, Kyoto and Maizuru, Japan (FAKU), and the Smithsonian Institution, National Museum of Natural History, Suitland, USA (USNM).

Careproctus tomiyamai sp. nov.

(New Japanese name: Fuji-kon’nyaku-uo)

(Figs. 15; Table 1)

Table 1 Counts and measurements of Careproctus tomiyamai sp. nov.

Holotype. MSM-18-91, 90.5 mm SL, male, Suruga Bay, southern Japan, ca. 800 m depth, 6 Apr. 2018, F/V Chokane-maru, bait trap.

Paratypes. BSKU 44396, 71.5 mm SL, female, Tosa Bay, southern Japan, 600 m depth, 10 Jan. 1988, R/V Kotaka-maru, bottom trawl; BSKU 48172, 81.5 mm SL, female, Tosa Bay, southern Japan, 600 m depth, 24 Mar. 1989, local F/V, bottom trawl; BSKU 86869, 72.5 mm SL, female, Hyuga-nada Sea, southern Japan (32°35.113′N, 132°12.993′E–32°34.582′N, 132°12.002′E), 790–808 m depth, 16 Dec. 1999, R/V Tansei-maru (KT-99-18), 3 m beam trawl.

Diagnosis. A species of Careproctus distinguished from all currently recognized congeners by the following combination of characters: total vertebrae 56–58; dorsal-fin rays 51 or 52; anal-fin rays 44–46; pectoral-fin rays 30–32; pyloric caeca 9–13; body slender, maximum depth 15.6–22.8% SL; teeth on both jaws strongly trilobed; pectoral fin shallowly notched, longest lower lobe ray 9.8–14.3% SL (46.0–60.4% HL); proximal pectoral radials 4 (3 + 1), upper portion of 1st and 3rd radials, and lower portion of 2nd radial notched; fenestrae in pectoral girdle 2, between scapula and 1st proximal radial, and 2nd and 3rd proximal radials; pelvic disk oval, wider than long, length 3.4–4.3% SL (14.2–19.3% HL), moderately to deeply cupped; peritoneum black in preserved specimens.

Description. Body slender, anteriorly rounded in cross section, becoming strongly compressed and tapering gradually posteriorly, deepest at dorsal-fin origin (Fig. 2). Skin smooth, lacking prickles; thin subdermal gelatinous layer present. Head small, 20.4–23.6% (20.4%) SL, dorsal profile rounded from nape to snout. Snout deep, slightly to moderately (moderately) projecting. Mouth terminal to subterminal (subterminal), horizontal when closed, oral cleft extending to anterior margin of orbit to pupil (anterior margin of pupil); maxilla extending to slightly anterior of to just mid-orbit (slightly anterior of mid-orbit). Lower jaw terminal, mandibular tooth plates exactly matching premaxillary tooth plates. Teeth on both jaws strongly trilobed; inner teeth larger than outer teeth (Fig. 3a). Premaxillary teeth in 16–20 (20) oblique rows of 3–7 (3–6) teeth, forming moderately narrow bands. Mandibular teeth in 15–18 (18) oblique rows of 3–7 (4–7) teeth, forming moderately narrow bands. Diastema absent at upper and lower jaw symphyses. Single nostril tube-like, level with mid-orbit. Orbit and eye sizes moderate, 24.9–28.0% (27.6%) HL and 21.7–27.6% (27.6%) HL, respectively. Dorsal contour of orbit below dorsal profile of head. Pupil round, widely open.

Fig. 2
figure 2

Lateral views of Careproctus tomiyamai sp. nov., holotype, MSM-18-91, 90.5 mm SL, male. a Line drawing of preserved specimen; b photograph of fresh specimen

Fig. 3
figure 3

Sketches of Careproctus tomiyamai sp. nov. a Premaxillary teeth (right side) of holotype, MSM-18-91; b pectoral girdle (right side) of paratype, BSKU 48172. C Coracoid, F fenestrae, PR proximal radials, S scapula

Cephalic pores small to moderate, similar in size or larger than nostril, nasal pores 2, maxillary pores 6, preoperculo-mandibular pores 7, suprabranchial pores 2; pore pattern 2-6-7-2. Coronal pore absent. Chin pores (= anteriormost preoperculo-mandibular pores) paired, opening directly on skin surface, well separated from each other. Free neuromasts absent.

Gill opening small, 24.3–32.5% (24.3%) HL, upper margin of slit level with upper margin of pupil to orbit (upper margin of orbit); lower margin of slit just above pectoral-fin base. Opercular flap rounded to slightly angular (rounded), supported by two spines weakly recurved dorsally; upper spine (from opercle) and lower spine (from subopercle) extending posteriorly to vertical through dorsal-fin origin.

Dorsal-fin rays 51 or 52 (52; Table 1), anterior rays slightly to moderately (moderately) buried in gelatinous tissue. Rayless predorsal bone absent. Anteriormost pterygiophore of dorsal fin bearing a single ray, inserted between 3rd–4th and 4th–5th (3rd and 4th) neural spines. Anal-fin rays 44–46 (44; Table 1), anterior rays slightly buried in gelatinous tissue. Anal-fin origin below 8th or 9th (9th) dorsal-fin ray base. Anteriormost pterygiophore of anal fin bearing a single ray.

Pectoral fin shallowly notched, with 30–32 (31) rays (Table 1). Uppermost pectoral-fin base at about 1/2 body depth, lowermost (= anteriormost) pectoral-fin base below mid-orbit to anterior margin of orbit (mid-orbit). Upper lobe rays slightly free from membrane at tip; 4th–7th (5th) ray from dorsalmost longest, reaching to below 7th–10th (8th) dorsal-fin ray base. Lower lobe rays more prominent than upper lobe rays; 5th–7th (5th) ray from ventralmost longest, nearly equal to somewhat longer than (nearly equal to) half of HL. Rays in notch more widely spaced than on either lobe, 8th–10th (9th) ray from ventralmost shortest, 63.7–75.0% (69.7%) length of longest ray in lower lobe. Proximal pectoral radials 4 (3 + 1), upper portion of 1st and 3rd radials, and lower portion of 2nd radial notched; fenestrae in pectoral girdle 2, present between scapula and 1st proximal radial, and 2nd and 3rd proximal radials (Fig. 3b). Scapula broad with stout helve, posteroventral portion notched. Coracoid triangular with thin helve and broad lamina. Distal radials apparently supporting 2nd–22th pectoral-fin rays.

Pelvic disk fleshy, oval, wider than long, length 14.2–19.3% (17.8%) HL, moderately to deeply (deeply) cupped, anterior lobe weakly developed (Fig. 4). Anus close to posterior edge of pelvic disk, vertically below nape region. Urogenital papilla conical, length 6.8–27.0% (7.6%) HL, located just behind anus. Stomach large, pouch-like. Pyloric caeca 9–13 (11; Table 1), length 20.1–30.2 (29.7%) HL, pointed at tips, located on left side of visceral cavity.

Fig. 4
figure 4

Ventral views of head and abdominal region of Careproctus tomiyamai sp. nov., holotype, MSM-18-91. a Fresh specimen; b preserved specimen

Caudal fin slightly emarginated, with 12 rays (Table 1), length 63.3–70.1% (68.6%) HL. Principal caudal-fin rays 10, dorsal procurrent ray 1, ventral procurrent ray 1 (Table 1). Membrane of posterior dorsal-fin rays continuous with caudal fin, overlapping 34.6–47.2% (47.2%) caudal-fin length. Membrane of posterior anal-fin rays continuous with caudal fin, overlapping 37.7–47.2% (47.2%) caudal-fin length. Hypural plates fused with terminal vertebral centrum, upper and lower plates separated by a wide slit. Single reduced epural present.

Vertebrae 56–58 (56), abdominal 10 or 11 (11), caudal 45–48 (45; Table 1). Pleural ribs slender, 2–4 pairs (4 pairs; Fig. 5); when 4 paired (in holotype, MSM-18-91), ribs on 8th–11th abdominal vertebrae, anteriormost paired ribs distinctly shorter than other ribs; when 3 paired (in two paratypes, BSKU 44396 and BSKU 86869), ribs on 8th–10th abdominal vertebrae, anteriormost paired ribs slightly shorter than other ribs; when 2 paired (in one paratype, BSKU 48172), ribs on 8th and 9th abdominal vertebrae, both paired ribs almost same in length. Epipleural ribs on 3rd–11th abdominal vertebrae, and 1st–5th (1st and 2nd) caudal vertebrae.

Fig. 5
figure 5

Radiographs of head and abdominal region of Careproctus tomiyamai sp. nov. a Holotype, MSM-18-91; b paratype, BSKU 44396; c paratype, BSKU 48172. Black or white arrows indicate pleural ribs

Color when fresh. Body pink, dorsal surface of head slightly darker with scattered black pigment. Basal parts of dorsal and anal fins, and pectoral fin pink. Distal margins of dorsal and anal fins, and caudal fin black. Pelvic disk white, except for sightly pinkish margin. Eye silvery; pupil black. Cephalic pores white. Belly visible through body wall silvery-white. Urogenital papilla black basally, white distally.

Color in alcohol. Fresh pinkish color of body, fins, and pelvic disk fading to pale white; black and white coloration of fins, pelvic disk, cephalic pores, and urogenital papilla unchanged, except pupil becoming pale; silvery coloration of eye and belly becoming black. Mouth cavity dusky. Orobranchial cavity and peritoneum black. Stomach and basal parts of pyloric caeca dusky to black (black); tips of pyloric caeca pale; intestine black.

Reproduction. Male (holotype, 90.5 mm SL) with enlarged testes, surface smooth, creamy-white in color. Females (all paratypes, 71.5–81.5 mm SL) with undeveloped blackish ovaries, containing evenly-sized immature eggs 0.3 mm in diameter.

Distribution. Known from the western North Pacific adjacent to southern Japan (south of Boso Peninsula, Chiba): Suruga Bay, Tosa Bay, and the Hyuga-nada Sea, in 600–808 m depth.

Etymology. The specific epithet “tomiyamai” is named for Shinichi Tomiyama (MSM), whose provision of the holotype of the new species initiated this study. The Japanese name Fuji-kon’nyaku-uo for the species reflects the translation of the Chinese characters for Dr. Tomiyama’s family name as “opulent mountain”, and can be associated with Mt. Fuji, which overlooks the holotype locality.


The holotype and paratypes of the new species differ slightly in some important but easily distorted characters, such as mouth position and proportional measurements of the abdominal region (e.g., ratio of distance from pelvic disk to anus). However, such differences have probably resulted from damage to the specimens during collection and subsequent preservation. Other measurements and all counts of meristic characters of the type specimens agreed closely, except for the number of pleural ribs (four pairs in holotype vs. two or three pairs in paratypes) (Fig. 5). Species with four paired pleural ribs were unknown in Careproctus, but this degree of difference in the number of pleural ribs (0–2 or 2–3) is recognized as a common intraspecific variation in Careproctus (see Orr et al. 2020; Murasaki et al. 2021b).

Careproctus tomiyamai clearly differs from the three other congeners from the Pacific coast of southern Japan in having 56–58 total vertebrae (vs. 60–63 in C. rhodomelas and 50 in C. surugaensis), 51 or 52 dorsal-fin rays (vs. 54–58 in C. rhodomelas, 47–50 in C. rotundifrons, and 47 in C. surugaensis), 44–46 anal-fin rays (vs. 48–51 in C. rhodomelas and 39 in C. surugaensis), 30–32 pectoral-fin rays (vs. 34–40 in C. rotundifrons), 9–13 pyloric caeca (vs. 15–29 in C. rotundifrons), short lower lobe pectoral-fin rays, 46.0–60.4% HL (vs. long, 90.0–128.0% HL in C. rhodomelas), and a moderate sized pelvic disk, length 3.4–4.3% SL (vs. large, 7.9% SL in C. surugaensis) (Sakurai and Shinohara 2008; Murasaki et al. 2017, 2021b; this study).

Among the species of Careproctus from the North Pacific, C. tomiyamai shares trilobed teeth, a shallowly notched pectoral fin, and black peritoneum (in preserved specimens) with Careproctus melanurus Gilbert 1892, Careproctus marginatus Kido 1988, and Careproctus ambustus Orr in Orr et al. 2020 (Kido 1988; Orr et al. 2020; this study). However, the new species is easily distinguished from them by its slender body, maximum depth 15.6–22.8% SL (vs. plump, maximum depth 25.4–32.2% SL in C. marginatus), and oval pelvic disk, being wider than long, and moderately to deeply cupped (vs. longer than wide, shallowly cupped in C. melanurus and C. ambustus) (Kido 1988; Orr et al. 2020; this study). Additionally, C. tomiyamai has 30–32 pectoral-fin rays (vs. 25–29 in C. marginatus), being relatively short in the lower lobe, 9.8–14.3% SL (vs. elongate, 12.9–24.9% SL in C. melanurus and C. ambustus), and 9–13 pyloric caeca (vs. 20–31 in C. melanurus, 24–35 in C. marginatus, and 23–36 in C. ambustus) (Stein 1978; Kido 1988; Kido and Shinohara 1997; Orr et al. 2020; this study). Careproctus tomiyamai is also similar to the two other species from the North Pacific, Careproctus simus Gilbert 1896 and Careproctus attenuatus Gilbert and Burke 1912b, by its slender body, trilobed teeth, and moderate sized pelvic disk (Mecklenburg et al. 2002; this study). However, the new species differs from them in having 51 or 52 dorsal-fin rays (vs. 54–60 in C. simus and 48 in C. attenuatus), 44–46 anal-fin rays (vs. 47–53 in C. simus and 40 in C. attenuatus), 9–13 pyloric caeca (vs. 19–28 in C. simus), and a shallowly notched pectoral fin (vs. deeply notched in C. attenuatus) (Mecklenburg et al. 2002; this study).

The new species has similarly shaped teeth and pectoral fin, and peritoneal coloration (in preserved specimens) to Careproctus novaezelandiae Andriashev 1990 (off southern New Zealand) and Careproctus paxtoni Stein, Chernova and Andriashev 2001 (off southeastern Australia) (Andriashev and Stein 1998; Stein et al. 2001; Stein 2012). However, C. tomiyamai is distinguished from both species by 30–32 pectoral-fin rays (vs. 34?–38 in C. novaezelandiae and 34–35 in C. paxtoni), and the absence of a fenestra between the 1st and 2nd proximal radials in the pectoral girdle (vs. present in both) (Andriashev and Stein 1998; Stein et al. 2001; Stein 2012).

The structure of the pectoral girdle of C. tomiyamai (see above description and Fig. 3b) is similar to that in Careproctus albescens Barnard 1927 from the eastern South Atlantic, a senior synonym of Careproctus griseldea Lloris 1982 (Andriashev 2003). However, both species are otherwise clearly distinct in total vertebral count (56–58 in C. tomiyamai vs. 60–63 in C. albescens) and teeth shape (strongly trilobed vs. simple) (Andriashev 2003).

Comparative materials. Careproctus rhodomelas: USNM 73334, holotype, off Bungo Channel, Japan, 741 m depth, 23 Aug. 1906; BSKU 20294, off eastern Miyakejima Island, Japan, 1,160 m, 14 Nov. 1972; BSKU 46963, Tosa Basin, Japan, 1,003 m, 8 Nov. 1989; BSKU 102864, Hatoma Knoll, southern Okinawa Trough, Japan, 1,530 m, 10 May 2005; MSM-20-65, Suruga Bay, Japan, 798 m, 12 Dec. 2012. Careproctus attenuatus: USNM 74386, holotype, photographs and radiographs only, Bering Sea, 715 m, 7 Jun. 1906. Careproctus surugaensis: MSM-17-81, holotype, Suruga Bay, 1,510 m, 28 Oct. 2015. Careproctus simus: FAKU S4927, Bering Sea, 515 m, 27 Sep. 1980; FAKU S4937, Bering Sea, 195 m, 3 Oct. 1980. Careproctus rotundifrons: MSM-14-15, Suruga Bay, 800 m, 23 Jan. 2013; MSM-15-81, MSM-15-82, Suruga Bay, 900 m, 7 Apr. 2007. Careproctus ambustus: MSM-22-9, off Iwate, Japan, 640 m, 3 Oct. 2018; FAKU S4827, FAKU S4828, Bering Sea, depth and date unknown.