Careproctus pellucidus Gilbert & Burke 1912

Careproctus pellucidus Gilbert & Burke 1912

English common name: Pellucid Snailfish Japanese common name: Ao-bikunin

Figures 2 B, 5E, 6; Tables 1–3

Careproctus pellucidus Gilbert & Burke 1912:366, pl. 44, fig. 3. Type locality: Off northeastern Honshu Island, 9°24'N, 141°52'30"E.— Burke 1930:134, fig. 54 (description, key).— Soldatov & Lindberg 1930:24 (key).— Chapman & DeLacy 1934:3 (comparisons).— Taranetz 1937:137 (Pacific Japan, key).— Hikita 1950:112 (list, northern Sea of Japan, = C. trachysoma or C. acanthodes ?).— Katayama 1952:97 (Sea of Japan, = C. trachysoma ?).— Böhlke 1953:136 (type catalog).— Matsubara 1955:1194 (Matsushima Bay, Japan).— Kato 1956:329 (Sea of Japan, list, = C. trachysoma ?).— Oshima 1957:4 (Sea of Japan, = C. trachysoma ?).— Takegawa & Morino 1970:387 (Sea of Japan, = C. trachysoma ?).— Ueno 1971:97 (Sea of Japan, Sakhalin, Pacific Japan, in part).—Kido 1984:339, pl. 365-I (Pacific coast of Japan).— Lindberg & Krasyukova 1987:448 (Sea of Japan, Sea of Okhotsk, and Pacific coast of Japan, in part).— Kido 1988:217 (considered C. pellucidus a synonym of C. rastrinus).— Tsuda 1990:514 (Sea of Japan, Pacific coast of Japan, in part).— Sheiko & Fedorov 2000:32 (considered C. pellucidus a synonym of C. rastrinus).— Mecklenburg et al. 2002:611 (considered C. pellucidus a synonym of C. rastrinus).— Chernova et al. 2004:13 (checklist).— Chernova 2005b:S7 (comparisons).—Love et al. 2005:103 (C. pellucidus valid).— Shinohara et al. 2009:721 (considered C. pellucidus a synonym of C. rastrinus).— Kai et al. 2011a:144 (genetics, morphology, phylogenetics, as “PAC1”).— Kai et al. 2011b:367 (genetics, as “PAC1”).

Holotype. USNM 73335, 107.0 mm, Japan, off Oshika Peninsula, northeastern coast of Honshu Island, 38.1567ºN, 141.875ºE, Albatross station 5048, depth 236 m, 10 September 1906.

Paratypes. SU 22378, 2 (47.0– 74.1 mm); USNM 74525, n = 1 [not seen]. Same data as for holotype.

Additional material examined. A total of 42 specimens, not including the types above, 92.6–213.9 mm SL. See “Non-type material examined below.”

Diagnosis. Careproctus pellucidus is distinguished from all other species of Careproctus by the combination of cytb and 16S rRNA sequences (“PAC1” of Kai et al. 2011a, b; Table 1), an anteriorly robust body covered by scattered cactus-like prickles, the presence of the postorbital pore, a moderate-sized pelvic disc, elongate lower pectoral-fin rays, and a light peritoneum. It is most similar to C. acanthodes of the western Pacific, from which it can be distinguished by its higher number of gill rakers (9–13 in C. pellucidus vs. 7–9 in C. acanthodes), smaller pelvic disc (10.0–17.0 vs. 18.2–28.8 % HL), longer lower pectoral-fin lobe (57.2–128.8 vs. 35.7–61.2 % HL), and larger gill slit (24.4–44.9 % HL, extending to pectoral-fin rays 5–10 vs. 18.2–36.1 % HL, extending to pectoral-fin ray 2). It is also similar to C. rastrinus and C. trachysoma, from both of which it can be distinguished by its typically lower counts of median fin rays (dorsal-fin rays 51–60, anal-fin rays 46–53 in C. pellucidus vs. 57–63 and 51–57 in C. rastrinus and C. trachysoma) and total vertebrae (57–63 vs. 62–67). It is further distinguished from C. spectrum by its smaller pelvic disc (10.0–17.0 vs. 22.5–23.1 % HL).

Description. Body heavy and deep anteriorly, tapering posteriorly, moderately compressed; depth at pectoralfin base 89.1–145.4 (103.8) % HL. Head large 21.7–32.0 (26.8) % SL and robust, dorsal profile rounded from nape to snout. Snout rounded, slightly projecting anterior to lower jaw. Mouth, small, subterminal, lower jaw included, horizontal; upper jaw 41.6–58.0 (47.6) % HL, maxilla extending to mid or posterior part of the orbit, oral cleft extending to anterior rim of orbit; mandible 41.6–58.0 % HL. Premaxillary tooth plates matching mandibular tooth plates. Premaxillary and mandibular teeth simple with weak shoulders in 26–48 oblique rows of 5–14 teeth forming narrow to broad bands. Diastema absent at symphysis of upper and lower jaws. Orbit large 25.0–40.0 (35.3) % HL, dorsal margin below dorsal contour of head, suborbital depth to upper jaw 31.6–67.5 (44.6) % OL; 10.8–18.2 (15.7) % HL; pupil round. Interorbital space broad, fleshy distance 37.3–60.1 (37.3) % HL, bony distance 21.4– 31.6 (29.8) % HL, strongly convex. Snout typically longer than orbit, 86.0–159.1 (143.1) % OL, 25.0–40.0 (32.6) % HL. Nostril single, with well-developed tube at level with mid-orbit; nostril tube length 1.0–7.3 % OL.

Pores of cephalic lateralis system of moderate size, pore pattern 2-6-7-2, chin pores paired. Interorbital pore absent.

Gill opening large, 24.4–45.0 (36.9) % HL, upper margin at level of lower part of orbit, extending ventrally to pectoral-fin ray 5–10 (ray 7). Opercular flap rounded to angular (rounded). Gill rakers 9–13, short, blunt.

Dorsal-fin rays 51–60 (55; Tables 2–3), anterior dorsal lobe absent, anterior rays buried in tissues, tips of more posterior rays not exserted. Anteriormost dorsal-fin pterygiophore inserted between neural spines 2 and 3 or 3 and 4, always rayless, second pterygiophore either rayless or bearing a single ray (between 3 and 4, second pterygiophore with ray). Predorsal length 25.0–35.1 (29.0) % SL. Anal-fin rays 46–53 (50; Tables 2–3), one to three anal-fin pterygiophores anterior to first haemal spine (two), each bearing a single ray, tips of rays not exserted. Anal-fin origin below vertebrae 12–13 (caudal vertebrae 2–3), preanal length 32.9–46.5 (32.9) % SL.

Pectoral fin deeply notched, with 30–37 (35) rays (Tables 2–3). Upper lobe 52.6–77.6 (52.6) % HL, with 21– 28 (27) rays extending beyond anus to or near anal-fin origin, shorter than lower lobe, dorsalmost rays lengthening to rays 5–7, more ventral rays gradually shortening to shortest ray of notch. Lower lobe elongate, 57.2–128.8 (73.4) % HL, with 6–10 rays (8), extending midway between anus and anal-fin origin to near anal-fin origin; dorsal rays gradually lengthening to elongate rays 4–5, ventral rays gradually shortening to ventralmost ray near pectoral symphysis. Tips of rays 5–50% free of membrane, rays of lower lobe more strongly exserted. Notch strong, rays in notch slightly more widely spaced than rays of lobes, more widely spaced ventrally. Uppermost pectoral-fin ray level with region between ventral rim of orbit and cleft. Insertion of lowermost pectoral-fin ray below anterior rim of orbit. Proximal pectoral radials four (3+1), moderately robust: radial 1 broadly hour-glass shaped with shallow notches; radial 2 hour-glass shaped, and radial 3 crescent shaped; radial 4 round (Fig. 5 E). Interradial fenestrae three, extending between scapula and proximal radials 1–3: fenestra 1 round, 2 oval, 3 dorsoventrally elongate. Scapula broadly T-shaped, with short robust arms and helve; coracoid with broad triangular head and short, robust helve. Distal radials present at base of rays 2–22, ventralmost at level of proximal radial 3, dorsalmost ray and more ventral rays articulating directly with pectoral cartilage.

Pelvic disc small, length 10.0–17.0 (14.8) % HL, round, about as long as wide, width 10.0–16.0 (13.8) % HL, anterior lobe weakly developed, slightly cupped, distance from tip of snout to pelvic disc 8.7–14.4 (11.4) % SL. Anus at level of posterior rim of orbit, close behind pelvic disc; distance from snout to anus 14.1–21.2 (18.1) % SL, 57.7–86.3 (67.6) % HL.

Principal caudal-fin rays 9–10, dorsal procurrent rays 1–2, ventral procurrent rays 1–2 (1–2 + 4–5/5 + 1–2) (1 + 4/5 + 1). Caudal fin 38.3–54.8 (42.2) % HL. Membrane of posterior dorsal- and anal-fin rays attached about equidistant to caudal fin: dorsal-fin rays attached to caudal fin 35.4–56.0 (45.8) % CL; anal-fin rays, 39.4–67.7 (54.2) % CL. Depth at base of caudal fin 10.0–14.9 (12.5) % CL.

Skin relatively thin, loose gelatinous layer beneath skin, cactus-like prickles scattered over body, in most dense region about 9 prickles in orbit length. Pyloric caeca 15–18 (18, Gilbert and Burke, 1912), length about 30–37 % HL, left side of visceral cavity.

Vertebrae 57–63 (60), precaudal 9–11 (10), caudal 47–53 (50; Tables 2–3). Pleural ribs 2 or 3 (3), anteriormost small and slender when 3, others long and slender, present on vertebrae 8–9 or 8–10 (8–10).

Coloration. Body and fins pink and white in life (Fig. 2 B); head, dorsum from nape to caudal fin, and ventrum at anal-fin origin to caudal fin dusky pink; isthmus, base of pectoral fin, and body posterior of gill slit to anal-fin origin lighter; area above belly silvery white (crystalline guanine) with orangish-pink highlights becoming obsolete at about anal-fin origin; base and lower lobe of pectoral fin white; dorsal margin and distal portion of fin pink; base of dorsal and anal fins pigmented along body margin; eye dark dorsally, silvery white ventrally. Body and fins pale in preservation; base of dorsal fin beneath skin with pigment, showing distinct line between fin and body. Peritoneum pale to lightly speckled; orobranchial cavity pale; stomach dark, intestines speckled, pyloric caeca pale, and urogenital papilla pale.

Life history. The largest specimen examined was a 213.9 mm male (HUMZ 67593). The smallest ripe female with yolked eggs was 132.9 mm; the largest, 175 mm. Egg diameters were 2.5–3.3 mm. One female was spent, with small white eggs 0.1–0.8 mm in diameter. The smallest ripe male examined was 136.1 mm; the largest, 140 mm.

Distribution. Careproctus pellucidus has been collected from the Pacific coast of Japan, off Hokkaido and northern Honshu (Fig. 6) at depths of 145 to 300 m.

Etymology. The specific epithet is derived from the Latin pellucidus, meaning “shining through”, referring to the species’ thin transparent skin.