A new snailfish of the genus Careproctus (Cottoidei: Liparidae) from the Pacific coast of southern Japan

A new snailfish, Careproctus tomiyamai, is described on the basis of four specimens collected from Suruga Bay, Tosa Bay, and the Hyuga-nada Sea, southern Japan (600–808 m depth). It is 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% standard length (SL); teeth on both jaws strongly trilobed; pectoral fin shallowly notched, longest lower lobe ray 9.8–14.3% SL [46.0–60.4% head length (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.


Introduction
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. This article was registered in the Official Registry of Zoological Nomenclature (ZooBank) as F68E4 3E6-217D-49CE-B70E-508FE 2A3D7 86.
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1 3 2011, 2018, 2021Machi et al. 2012;Nakabo and Kai 2013;Orr et al. 2015Orr et al. , 2020Murasaki et al. 2017;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 2008Murasaki et al. 2017Murasaki et al. , 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.

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).
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.
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.
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.

Discussion
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).
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).
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