Paraliparis mandibularis Kido, 1985

Kai, Yoshiaki, Murasaki, Kenta, Misawa, Ryo, Fukui, Atsushi, Morikawa, Eisuke & Narimatsu, Yoji, 2020, A new species of snailfish of the genus Paraliparis (Liparidae) from the western North Pacific, with a redescription of the poorly known species Paraliparis mandibularis, ZooKeys 968, pp. 143-159 : 143

Paraliparis mandibularis Kido, 1985 Figs 3B, D , 6 [Japanese name: Ago-inkiuo]

Paraliparis mandibularis Kido 1985: 362, figs 2-4, Tosa Bay, Kochi, Japan; Kido 1988: 234, fig. 57 (modified from Kido 1985); Shinohara et al. 2001: 320, listed, Tosa Bay, Kochi, Japan; Nakabo and Kai 2013: 1217, key, unnumbered fig., Tosa Bay, Kochi, Japan.

Materials examined.

BSKU 30513 (holotype of P. mandibularis ), 103.6 mm SL, 32.967°N, 133.533°E, 605 m depth, Tosa Bay, Kochi, Japan; BSKU 43451, 128.1 mm SL, 32.545°N, 132.433°E, 1,075-1,092 m depth, off Bungo Channel, Ehime, Japan; BSKU 44260, 44262, 44267, 44269 (C&S), 44397, 44398, 111.4-119.1 mm SL, 600 m depth, Tosa Bay, Kochi, Japan.

Diagnosis.

Paraliparis mandibularis is distinguished from other species of Paraliparis by the following combination of characters: mouth oblique; uppermost pectoral-fin base below a horizontal through posterior margin of maxillary; 63-66 vertebrae, 58-61 dorsal-fin rays, 52-54 anal-fin rays, 6 principal caudal-fin rays, and 27-30 pectoral-fin rays. Proximal pectoral radials 4, enlarged and moved to anterior edge of basal lamina. Parietals present. Among North Pacific species, it is similar to P. flammeus sp. nov., which differs from the former in having 17-20 pectoral-fin rays, and to P. mento , which has 5 principal caudal-fin rays.

Description.

Measurements are shown in Table 1 . Body compressed, elongate, deepest at nape, taping posteriorly (Fig. 5 ). Skin thin, fragile. Head compressed, dorsal profile strongly sloping from nape to snout. Snout deep, abruptly angled, its length almost equal to orbit diameter; not projecting anterior to upper jaw. Mouth strongly oblique, lower jaw slightly protruding beyond (or almost same length as) upper jaw; premaxillary tooth plates matching mandibular tooth plates; maxilla extending to posterior margin of orbit; oral cleft extending to middle of orbit. Premaxillary teeth simple, in 3-6 oblique rows; diastema narrow between premaxillae. Mandibular teeth simple, in 4 or 5 oblique rows (Fig. 3B ); diastema absent at lower jaw symphysis. Orbit of moderate size, rounded. Nostril single, without distinct tube, slightly above level of mid-orbit. Cephalic sensory pores small: nasal pores 2, maxillary pores 6, preoperculomandibular pores 7, suprabranchial pore 1; cephalic pore pattern 2-6-7-1. Chin pores paired, openings well separated on skin surface. Coronal pore absent. Gill slit moderately large, upper margin level with mid-orbit, extending ventrally to just above pectoral fin or to level of 1-3 uppermost pectoral-fin rays. Gill rakers 10-12, blunt and small. Tip of opercular flap sharp, directed posteriorly, level with mid-orbit or posterior margin of maxillary.

Dorsal-fin rays 58-63; anteriormost ray above tip of opercle, posteriormost ray attached membranously to dorsalmost caudal-fin ray. Anteriormost dorsal-fin pterygiophore inserted between neural spines 3 and 4 or 4 and 5, bearing a single ray. Anal-fin rays 52-54; posteriormost ray attached membranously to ventralmost caudal-fin ray. Vertebrae 63-66, comprising precaudal 9 and caudal 54-57. Pleural ribs absent. Hypurals and parhypural fused into single plate. Caudal fin slender, posterior margin slightly rounded. Principal caudal-fin rays 6, dorsal principal rays 3, ventral principal rays 3, no procurrent rays. Pyloric caeca 5 or 6, short and finger-like, on left side of visceral cavity. Anus below posterior margin of orbit.

Pectoral fin moderately notched, with 27-30 rays; upper lobe with 17-19 rays, extending beyond (or just reaching) anal-fin origin; lower lobe elongate, with 8-13 rays, uppermost ray of lower lobe longest, extending beyond anus, not reaching anal-fin origin. Uppermost pectoral-fin base below a horizontal through posterior margin of maxillary. Lowermost pectoral-fin base below anterior rim of orbit or below midway between tip of snout and anterior rim of orbit. Rays between upper and lower lobes widely spaced.

Selected osteological characters. Roof of cranium without distinct crest comprising well ossified frontals, supraoccipital, and parietals. Opercle well ossified, sharpened posteriorly, supporting upper margin of opercular flap. Subopercle thin, comprising two spines forming a V-shape; lower spine supporting lower margin of opercular flap. Subopercle and interopercle attached. Cleithrum broad and robust, dorsal portion elongated. Proximal pectoral radials 4, enlarged occupying almost entire width of cartilaginous basal laminae and moved to anterior edge of basal lamina (Fig. 3D ). No interradial fenestrae between proximal radials. Scapula with strong helve. Coracoid narrowly triangular with narrow lamina. Distal radials absent.

Coloration. In fresh specimens, head and body pale pink, posterior half of body reddish; dark peritoneum visible through thin skin; dorsal and anal fins pale pink, distally reddish; caudal and pectoral fins red (Fig. 6 ). In preserved specimens, head, body, and fins pale; peritoneum black, stomach pale or white; orobranchial cavity pale with scattered melanophores.

Geographical distribution.

Western Pacific Ocean; Tosa Bay and Bungo channel, off Shikoku Island, Japan, in depths of 600-1,092 m ( Kido 1988; this study).

Remarks.

Paraliparis mandibularis was originally described by Kido (1985) on the basis of a single specimen collected from Tosa Bay, Japan. Subsequently, Kido (1988) redescribed the species on the basis of the holotype and an additional non-type specimen. However, a number of details, including osteology and fresh coloration have remained unknown to date. Whereas the pectoral girdle in Paraliparis species generally has a reduced number and size of radials ( Andriashev 1998; Orr et al. 2019), that of P. mandibularis has four broad robust radials (Fig. 3D ). The species is also characterized by a pair of parietals in the cranium, such being absent in some other species of Paraliparis ( Kido 1988). Although Kido (1988) described P. mandibularis as having a diastema at the symphysis of both the upper and lower jaws, we could find no obvious diastema at the lower jaw symphysis in the specimens examined here, including the holotype. In addition to the differences described above between P. mandibularis and P. flammeus , the former is further distinguished from the latter by the enlarged pectoral radials occupying almost entire width of the cartilaginous basal laminae and moved to the anterior edge of basal lamina in the pectoral girdle (vs moderately large and medial) and the parietals in the cranium (vs. absent). Paraliparis mandibularis differs from other species with an oblique mouth and a low positioned pectoral fin, viz. P. angustifrons , P. membranaceus , and P. molinai (see Remarks under P. flammeus ), in having 27-30 pectoral-fin rays (vs 37 in P. angustifrons , ca 25 in P. membranaceus , 24 in P. molinai ). Paraliparis membranaceus and P. molinai have similar pectoral-fin ray numbers to P. mandibularis but have a reduced caudal fin (4 rays in P. molinai , 2 or 3 in P. membranaceus vs 6 in P. mandibularis ) ( Stein 2005).

Figures

Figure 3. A, B teeth on lower jaw C, D pectoral girdle A, C Paraliparis flammeus sp. nov., FAKU 147158, paratype, 61.2 mm SL B, D P. mandibularis, BSKU 44286, 110.0 + mm SL. Abbreviations: S, scapula; PR, proximal radials; C, coracoid; DR, distal radials. Scale bars: 0.5 mm (A, B); 5 mm (C, D).

Figure 5. Maximum likelihood phylogenetic tree of Paraliparis and related genera based on COI sequences (492 bp). Support values (≥ 50 % ML bootstrap probability) indicated along branches. Each node labeled with a registration number (red, determined in this study) or an accession number deposited in INSDC or BOLD. Nectoliparis pelagicus included as out-group.

Figure 6. Paraliparis mandibularis, BSKU 43451, 128.1 mm SL, fresh specimen. Photo by BSKU.