Apristurus breviventralis Kawauchi, Weigmann & Nakaya, 2014, sp. nov.

Apristurus breviventralis sp. nov.

Proposed common name: Shortbelly catshark (Figures 1–9, Table 1)

Holotype: ZMH 25600, mature male, 444 mm total length (TL) in fresh state, 439 mm TL in 70% ethanol preserved, RV ‘Vityaz’, cr. 17, sta. 2565, 28 October 1988, 12°22’8”N, 53°02’7”E – 12°21’2”N, 53°01’3”E, 1000–1120 m depth, 29 m shrimp trawl, trawl # 5, on the bottom for 62 minutes, off Socotra Islands.

Paratypes: 8 specimens. ZMH 25601, 1 immature male and 5 mature males, 344–485 mm TL in fresh state, 337–477 mm TL in 70% ethanol preserved, same data as holotype; HUMZ 221300, mature male, 444 mm TL in fresh state, 440 mm TL in 70% ethanol preserved, same data as holotype; HUMZ 221301, mature male, 474 mm TL in fresh state, 467 mm TL in 70% ethanol preserved, same data as holotype.

Diagnosis. A species of the ‘ brunneus group’ of Apristurus with: upper labial furrows clearly longer than lower ones; first dorsal fin much smaller than second dorsal fin, originating distinctly posterior to level of pelvicfin insertion; second dorsal-fin insertion clearly anterior to level of anal-fin insertion; snout moderately long, its tip pointed; pre-outer nostril length slightly greater than internarial width, about 0.6–0.8 times interorbital width; abdomen very short; pectoral-pelvic space much shorter than anal-fin base length; pectoral-fin tip posterior to level of midpoint of pectoral-pelvic space; 17–19 spiral valves; 33–36 monospondylous and 34–38 precaudal diplospondylous vertebrae; small dermal denticles giving a velvety texture to body surface; no enlarged dermal denticles along dorsal margin of caudal fin; claspers without hooks, posterior margin of exorhipidion forming a free lobe; body and fins uniformly medium or dark brown.

Description of the holotype (counts and measurements of paratypes are given in parentheses, if different). Morphometric measurements and meristic counts are given in Table 1.

Body (Figure 1) cylindrical, slender, and elongate. Head (Figure 2) depressed, posterior part of body compressed laterally. Snout moderately long, tip pointed. Pre-outer nostril length slightly greater than internarial width and about 0.6 (0.6–0.8) times interorbital width. Pre-oral length slightly less than pre-orbital length, about 2.3 (2.4–2.9) times internarial width, slightly less than mouth width, and about 1.3 (1.3–1.5) times interorbital width. Pre-orbital length about 1.4 (1.4–1.7) times interorbital width and about 2.4 (2.4–2.7) times orbit length. Internarial width nearly equal to orbit length and nostril length, respectively. Nostrils oblique, expanding diagonally inwards from snout edge; nostril length about 0.6 (0.5–0.6) times pre-inner nostril length, about 1.1 (1.1–1.4) times internarial width, and about 1.0 (0.9–1.2) times orbit length. Nostril-mouth space about 0.6 (0.5–0.7) times internarial width. Mouth widely arched, with well-developed labial furrows; upper labial furrows about 1.5 (1.3–1.6) times longer than lower ones. Upper labial furrows reaching beyond midpoint between mouth corner and posterior margin of nostril.

Orbits moderately large, without distinct subocular folds; orbit length about equal to internarial width and about 0.6 (0.5–0.7) times interorbital width. Spiracles small, their length about 0.2 (0.1–0.2) times orbit length, situated slightly below level of horizontal axis of orbits. Five small gill slits present; 4th gill slit above pectoral fin origin; 5th gill slit smallest. Gill septa without projections, covered with densely-set dermal denticles.

Abdomen very short; pectoral-pelvic space much shorter than anal-fin base length and almost equal to interdorsal space; pectoral-fin tips reaching 5/7 of pectoral-pelvic space. Pectoral fins large, wide, and subtriangular; length of anterior margin almost equal to distance between pectoral- and pelvic-fin origins, anterior margin not parallel to inner margin; right and left fins separated by a space of half anal-fin height. Pelvic fins moderately large; pelvic-fin length about twice anal-fin height. Dorsal fins similar in shape. First dorsal fin much smaller than second dorsal fin, about half in size; origin posterior to level of pelvic-fin insertion; insertion posterior to level of anal-fin origin (ceratotrichia). Second dorsal-fin origin slightly posterior to anal-fin midbase; insertion slightly anterior to anal-fin insertion. Anal fin relatively high, somewhat triangular; base much longer than pectoral-pelvic space and almost equal to pre-branchial length; apex clearly posterior to level of first dorsal-fin insertion; posterior margin straight; anal and caudal fins separated only by a notch. Caudal fin slender; ventral lobe high; apex of ventral lobe rather angular; subterminal notch distinct; terminal lobe moderately long, about 1.9 (1.7–1.9) times as long as high. Caudal peduncle high, height about half of interdorsal space.

...... continued on the next page Teeth (Figure 3) numerous and small; upper anterior and upper lateral teeth with a long, robust central cusp and one or two short, sharp lateral cusps on each side of the central cusp; lower anterior and lower lateral teeth with a long, robust central cusp and two or three short lateral cusps on each side of the central cusp.

Dermal denticles (Figure 4) on dorsolateral side of body small, overlapping each other, tricuspidate with a moderately long, ridged central cusp and a shorter lateral cusp on each side of the central cusp; outer surface of denticles completely structured by reticulations (Figure 4 A, B). Dermal denticles of immature male paratype similar to those of the adult type specimens, but less densely set, more slender, and with less deep surface structure (Figure 4 C, D). No enlarged dermal denticles along dorsal margin of caudal fin. Densely-set dermal denticles present around gill slits and on gill septa.

Claspers (Figure 5) long, stout at base, tapering towards posterior tip; ventral and outer lateral sides covered with dermal denticles. Dorsal side of clasper naked, ventral and lateral sides covered with clasper denticles; clasper hooks absent; pseudosiphon slit-shaped and deep; cover rhipidion reduced; envelope large, tapering towards pseudosiphon. Pseudopera not distinctively long; exorhipidion moderately large and simple, with posterior end free.

Size: maximum size of males at least 477 mm TL, females unknown. Maturity in males: the smallest paratype (337 mm TL) with short and soft claspers of 2.5% TL, and ranked as immature (maturity stage 1); holotype and other paratypes (432–477 mm TL) mature (maturity stage 3) with long, fully developed claspers (5.8–8.1% TL).

Color in preservative. Upper and lower surfaces of body and fins uniformly medium or dark brown. Tongue and palate light brown, peritoneum light brown.

FIGURE 3. Teeth of Apristurus breviventralis sp. nov., paratype, HUMZ 221300, mature male, 440 mm TL: A: 8th upper anterior tooth on right side, B: 17th upper lateral tooth on right side, C: 5th lower anterior tooth on right sight, D: 17th lower lateral tooth on left side. Scale bar = 200 µm.

Distribution (Figure 6). Off the Socotra Islands, Gulf of Aden; collected from the insular slope in 1000–1120 m depth.

Etymology. The specific name breviventralis is derived from the short abdomen of the species (lat. brevis = short, ventralis = pertaining to the abdomen).

Remarks. Apristurus breviventralis sp. nov. belongs to the ‘ brunneus group’ of Apristurus sensu Nakaya & Sato (1999) due to having a pre-outer nostril length shorter than interorbital width, a high spiral valve count, upper labial furrows longer than the lower ones, and discontinuous supraorbital sensory canals. The ‘ brunneus group’ presently comprises the following 20 valid species: Apristurus brunneus (Gilbert, 1892); A. indicus (Brauer, 1906); A. macrorhynchus (Tanaka, 1909); A. platyrhynchus (Tanaka, 1909); A. sibogae (Weber, 1913); A. laurussonii (Saemundsson, 1922); A. saldanha (Barnard, 1925); A. nasutus de Buen, 1959; A. investigatoris (Misra, 1962); A. japonicus Nakaya, 1975; A. canutus Springer & Heemstra, 1979; A. parvipinnis Springer & Heemstra, 1979; A. sinensis Chu & Hu, 1981; A. gibbosus Meng, Chu & Li, 1985; A. macrostomus Chu, Meng & Li, 1985; A. micropterygeus Meng, Chu & Li, 1986; A. internatus Deng, Xiong & Zhan, 1988; A. exsanguis Sato, Nakaya & Stewart, 1999; A. melanoasper Iglésias, Nakaya & Stehmann, 2004; A. nakayai Iglésias, 2012.

Apristurus breviventralis sp. nov. is distinguished from A. brunneus, A. exsanguis, A. gibbosus, A. indicus, A. internatus, A. investigatoris, A. japonicus, A. laurussonii, A. macrorhynchus, A. macrostomus, A. melanoasper, A. nasutus, A. parvipinnis, A. saldanha, and A. sinensis by having the following characters: pectoral-fin tip extending far beyond the midpoint between the paired fin bases, pectoral-pelvic space much shorter than the anal-fin base (ceratotrichia), anal fin low with a long base (also applicable for A. indicus), and first dorsal-fin origin located posterior to level of midpoint of pelvic-anal space. Apristurus breviventralis sp. nov. is also clearly separable from A. micropterygeus by having a brush-shaped first dorsal fin (vs. a narrow and sharply pointed first dorsal fin in A. micropterygeus) and from A. sibogae by the second dorsal-fin insertion situated clearly anterior to the anal-fin insertion (vs. posterior to anal-fin insertion in A. sibogae).

Apristurus breviventralis sp. nov. resembles A. platyrhynchus from the Indo-West Pacific Ocean, A. nakayai from New Caledonia, and A. canutus from the western Atlantic Ocean in the aforementioned characters. However, the new species is clearly distinct from A. platyrhynchus and A. nakayai due to having longer claspers in adults (5.8–8.1% TL vs. 4.5–5.7% TL in A. platyrhynchus and 5.0% TL in A. nakayai; Figure 7). Furthermore, the new species is a small-sized species, maturing at a size of less than 432 mm TL, whereas A. platyrhynchus is completely immature at such sizes and gets mature at about 600 mm TL, indicating a large-sized species. A. nakayai is also a large-sized species as the only known, mature male specimen has 676 mm TL (Figure 8). Apristurus breviventralis sp. nov. and A. canutus are small-sized species, both maturing around 400 mm TL, but the new species is distinguishable in having greater nostril length than internarial width (vice versa in A. canutus; Figure 9). Furthermore, the new species has longer claspers in adults (5.8–8.1% TL vs. about 4% TL in A. canutus; Figure 7).