Careproctus sp. cf. gilberti

Kai, Yoshiaki, Matsuzaki, Koji, Mori, Toshiaki, Pitruk, Dmitry L., Misawa, Ryo & Tashiro, Fumihito, 2024, Snailfishes of the genus Careproctus (Perciformes: Liparidae) with a reduced pelvic disk: three new species and new records from the western North Pacific with comments on their phenotypic diversity, Zootaxa 5492 (2), pp. 191-213 : 206-209

Careproctus sp. cf. gilberti

Fig. 7C ; Table 2

This species is represented only by a single specimen that is not genetically distinct from C. gilberti sensu stricto. Therefore, we refrain from formally describing and naming it.

Materials examined. FAKU 147753 , 55.1 mm SL, sex undetermined, 41.7713ºN, 142.8075ºE, 550 m depth, 9 Jun. 2017, R / V Wakataka-maru.

Description. Counts and measurements shown in Table 2 .

Body slender, moderately compressed, tapering posteriorly, deepest at nape ( Fig. 7c ). Skin thin, naked (without cactus-like prickles); gelatinous tissue under skin not developed. Head moderately large, dorsal profile gradually sloping from nape to snout. Snout moderately deep, not protruding anterior to mouth. Mouth large, terminal, horizontal; maxilla extending to posterior rim of orbit; oral cleft extending to mid-orbit. Premaxillary teeth sharp, simple, arranged in oblique rows of 5 teeth per row forming relatively narrow band, inner teeth enlarged. Mandibular teeth sharp, simple, arranged in oblique rows of 6 teeth per row forming narrow band, inner teeth not enlarged. Diastema at symphysis of upper jaws V-shaped, wider anteriorly, that of lower jaws narrow. Orbit of moderate size, rounded; pupil rounded. Nostril single, with short tube, level with mid-orbit. Cephalic sensory pores of moderate size: nasal pores 2, maxillary pores 6, preoperculomandibular pores 7, suprabranchial pores 2; cephalic pore pattern 2-6-7-2. Chin pores paired in separate pits, well separated. Coronal pore absent. Gill slit moderately large, upper margin level with mid-orbit, extending ventrally to pectoral-fin ray 8. Opercular flap angular, pointed posteriorly; tip level with ventral rim of orbit. Pyloric caeca 16, thick, covering half of stomach, on center-left side of visceral cavity.

Vertebrae 63, precaudal 9 and caudal 54. Pleural ribs in 2 pairs, on abdominal vertebrae 8 and 9. Dorsal-fin rays 57, not exserted. Anteriormost dorsal-fin pterygiophore inserted between neural spines 4 and 5, bearing a single ray. Anterior rayless pterygiophore absent. Anal-fin rays 53, not exserted. Two anal-fin pterygiophores anterior to 1 st haemal spine, each bearing a single ray. Membrane of posterior dorsal- and anal-fin rays attached about equidistant to caudal fin. Caudal fin slightly rounded. Principal caudal-fin rays 8, 4 and 5 rays on upper and lower hypurals, respectively, dorsal and ventral procurrent rays 1 each. Hypural plates fused with terminal vertebral centrum and parhypural, upper and lower hypural plate separated by narrow slit.

Pectoral fin deeply notched, with 33 rays; upper lobe with 24 rays, reaching to anal-fin ray 5; lower lobe elongate, with 9 rays, 6 th ray from ventralmost longest, slightly longer than upper lobe, below tip of opercular flap. Rays in notch more widely spaced than rays of lobes. Uppermost pectoral-fin base level with mouth corner. Lowermost pectoral-fin base below mid-orbit. Pelvic disk rounded, minute. Anus much closer to pelvic disk than to anal fin origin, located below posterior rim of orbit.

Coloration: Fresh coloration unknown. When preserved, head, body, and fins white. Eyes black. Oral and branchial cavities pale; peritoneum and stomach black.

Distribution. Currently known only from the Pacific coast of Hokkaido from a depth of 550 m.

Remarks. The gill rakers and pectoral girdle are not investigated for the specimen. Careproctus gilberti is characterized as follows: vertebrae 57–58 (10 + 47–48); dorsal-fin rays 49–55; anal-fin rays 44–48; pectoral-fin rays 30–35; pectoral fin deeply notched, lower lobe longer than upper lobe; pelvic disk small, rounded or subtriangular; cephalic pores 2-6-7-2, chin pores paired in separate pits; gill slit large, extending ventrally to pectoral-fin rays 14–16; teeth simple or slightly shouldered; stomach black (Burke 1912; Stein 1978; Mecklenburg et al. 2002; this study) ( Fig. 7D, E ; Table 2 ). The present specimen agreed closely with the holotype of C. gilberti and other specimens from the Aleutian Is. in having a long pectoral fin lower lobe, no cactus-like prickles on the skin, and a black stomach (Burke 1912; Stein 1978; Mecklenburg et al. 2002; this study) ( Tables 1 , 2 ). However, the counts of vertebrae, dorsal- and anal-fin rays, and pyloric caeca of the former were different from those of the holotype and Aleutian specimens of C. gilberti . In addition, the black peritoneum of the former clearly contrasted with the pale or silvery peritoneum with dots in the latter. However, the COI sequence of the present specimen had an identical haplotype with specimens from the Aleutian Is., determined by Orr et al. (2019) ( Fig. 8 ). Therefore, we refrain from formally describing and naming this species based on a single specimen and, for the time being, consider it to be an unidentified Careproctus species closely related to C. gilberti . Careproctus gilberti has been previously recorded from Attu Island, western Aleutian Is. eastward to California ( Stein 1978; Mecklenburg et al. 2002), and was suggested as occurring at the Commander Islands, west of the Kamchatka Peninsula by Parin et al. (2014), but without evidential specimens. The present specimen was collected from the Pacific coast of Hokkaido, Japan, some 2,500 km eastward from Attu Island. Although a principal components analysis of morphometric measurements placed the specimen close to C. spinulosus sp. nov., somewhat distant from C. gilberti ( Fig. 9 ; see also Results and discussion Section), the former clearly differed from the latter in having higher counts of vertebrae, and dorsal- and anal-fin rays ( Tables 1 , 2 ).

Careproctus gilbert is sometimes confused with C. ostentum ( Fig. 7A ), as noted by Mecklenburg et al. (2002), but the two species were differentiated in the COI sequences ( Fig. 8 ). Morphologically, C. gilberti can be distinguished from C. ostentum in having a larger pelvic disk and lower pectoral fin lobe, being longer than the upper lobe (vs. shorter than the upper lobe) ( Table 2 ). The two species also differed in the shape of the diastema at the upper jaw symphysis: V-shaped in C. ostentum and a narrow slit in C. gilberti . It should be noted that the presently described specimen of Careproctus sp. cf. gilberti was similar to C. ostentum in diastema shape.

Careproctus parvidiscus and C. longibarbatus sp. nov. are also similar to Careproctus sp. cf. gilberti in having a moderately long lower pectoral-fin lobe (12.3% and 10.3–16.1% of SL, respectively) and black stomach, as well as a rudimentary pelvic disk ( Fig. 6E ). However, the counts of vertebrae, and dorsal- and anal-fin rays of C. parvidiscus (57, 50, and 44, respectively) were much lower than those of “ Careproctus sp. cf. gilberti ” (63, 57, and 53, respectively) ( Table 2 ). Although the latter counts fell into the ranges of C. longibarbatus sp. nov. counts, the former species had a much smaller gill slit, extending ventrally to pectoral-fin ray 8 (vs. extending ventrally to pectoral-fin rays 12–19 in C. longibarbatus sp. nov.).

Comparative materials. Careproctus gilberti : USNM 64110 , holotype, 73.0 mm SL, male, Shelikof Strait north of Cape Uyak , Kodiak Island, Alaska, USA, Albatross station 4292, depth 102 fathoms ; FAKU S4826 , S4869 , S4870 , S4873 , 68.5–70.3 mm SL, 3 females (one sex undetermined), Bering Sea (no further data) ; OS 8684 , 65.8– 69.2 mm SL, female (one sex undetermined), 51.725ºN, 175.615ºW .

Figures

FIGURE 6. Careproctus mederi, FAKU 146572, 102.3 mm SL, (preserved) (A); diastema at symphysis of upper jaw of FAKU 148478, 143.6 mm SL (B); eggs of FAKU 146572 (C); one of four syntypes of ZIN 18958, 150.0 mm SL, (preserved) (D), eggs (E), and ventral view of head region (F). Dotted red line and arrow indicates position of anus and pelvic disk, respectively.

FIGURE 7. Careproctus gilberti and related species. Careproctus ostentum, UW 150870, 72.1 mm SL, (preserved) (A); C. parvidiscus, HUMZ 164407, holotype, 167.7 mm SL, (preserved) (B); Careproctus sp. cf. gilberti, FAKU 147753, 55.1 mm SL, (preserved) (C); C. gilberti, OS 8684, 69.2 mm SL, (preserved) (D), and ventral view of head region of OS 8684 (E).

FIGURE 8. (A): Neighbor-joining (NJ) tree of the Careproctus gilberti, C. rastrinus, and C. reinhardti species groups based on sequence variations in the mitochondrial COI (474 bp) gene. Support values (≥50% ML bootstrap probability) indicated along branches. Each node labeled with collection registration number (sequences determined here) or INSDC accession number (sequences determined in previous studies, in italics). (B): A minimum spanning network of the C. gilberti species group. Each circle represents a unique haplotype; area of each circle proportional to number of individuals; each bar on internal nodes represents a single nucleotide change. In addition to the sequences determined here, the following sequences from INSDC were used. Careproctus ostentum: MH715573, KU053754; C. gilberti: MH630293, KU053753, MH715534–MH715569, MH882481, JQ354029, MH630294.

FIGURE 9. Plots of scores of principal components 1 and 2 based on 13 size-corrected measurements of the Careproctus gilberti species group only (A), and the C. gilberti + C. rastrinus + C. reinhardti species groups (B). Distributions of PC1 and PC2 scores for the C. gilberti species group and for C. rastrinus + C. reinhardti species groups are shown in each axis of (B).