Bythaelurus tenuicephalus Kaschner, Weigmann & Thiel, 2015, n. sp.
Creators: name: Kaschner, Carina Julia
name: Weigmann, Simon
name: Thiel, Ralf
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Elasmobranchii
Carcharhiniformes
Scyliorhinidae
Bythaelurus
Bythaelurus tenuicephalus

description: Bythaelurus tenuicephalus n. sp.
(Narrowhead Catshark)
Figures 3–11; Table 1
Scylliorhinus hispidus: Brauer, 1908: 7 –8.
Halaelurus lutarius: Springer & D’Aubrey, 1972: 6 –8; Bass et al., 1975: 11 –12, Springer, 1979: 82 –83.
Holotype. ZMH 10163, adult male, 279 mm TL, RV ‘Valdivia’, station 245, off North Tanzania, 5°27'9" S, 39°18'8" E, 463 m depth, 22 March 1899.
Paratype. ZMH 26070, juvenile male, 291 mm TL fresh, 285 mm TL 70% ethanol preserved, RV ‘Vityaz’, cruise 17, station 2622, off South Mozambique, 21°12'8" S, 35°41'8" E – 21°16'6" S, 35°41'3" E, 490–550 m depth, 29 m shrimp trawl, trawl # 25, on the bottom for 63 minutes, 21 Nov 1988.
Diagnosis. A very small scyliorhinid species with the following characteristics: body firm and elongated; snout long (preorbital length 6.7–7.1% TL) and slender, only slightly bell-shaped in dorsoventral view without distinct lateral indention; pre-outer nostril length 1.2 times internarial space; preorbital snout length 1.0–1.4 times interorbital space; preoral snout length 1.3–1.4 times in mouth width; eye length 14.0–15.3 times in predorsal distance, 6.0–7.0 times in head length and 1.7–1.8 times eye height; head length 2.7–3.1 times width at level of maximum outer extent of anterior nostrils; head width at level of maximum outer extent of anterior nostrils only 1.2 times width at level of lateral indention of head, equal to preorbital length, and 7.2–7.3% TL; tongue and roof of mouth loosely set with oral papillae of distinct size; pelvic anterior margin 1.9–2.1 times in pectoral fin anterior margin; first dorsal fin base 1.9 times in interdorsal space; length of second dorsal fin inner margin 1.4 times in second dorsal fin height; second dorsal-fin base length 5.9–6.9% TL; anal-fin base 0.9–1.1 times interdorsal space. Coloration in preservative: bicolored with an abrupt lateral demarcation of medium brown dorsal and whitish ventral color, about five indistinct darker blotches on dorsolateral surface at gill slits and dorsal and caudal fins; fins lighter towards their margins; upper jaw with 67–76 and lower jaw with 62–64 rows of small tricuspidate teeth; monospondylous trunk vertebrae centra 38–40, diplospondylous precaudal centra 43–50, total centra about 133–138.
Description of holotype (Figures 3–11). Values of the paratype are given in parentheses if differing. Morphometric measurements and meristics are given in Table 1.
External morphology. Body firm and elongated, subcircular in cross section at mid-trunk, laterally compressed and tapering posterior to anus; head region slender, long abdominal and caudal sections (Figures 3–5). No predorsal, interdorsal, or postdorsal ridges; no postanal ridge; no lateral ridges. Trunk slightly shorter than tail, distance from tip of snout to anterior cloaca 46.2% (42.9%) TL; pre-first dorsal-fin length 48.3% (46.1%) TL, presecond dorsal-fin length 63.3% (63.2%) TL, precaudal length 71.3% (68.6%) TL. Head slender and with a broadly pointed snout; laterally slightly compressed in gill region (Figures 6–7); no supraorbital crest on chondrocranium; head length 3.1 (2.7) times width at level of maximum extent of anterior nostrils and 1.3 (1.2) times pectoral-pelvic space; head width at level of maximum outer extent of anterior nostrils only 1.2 times width at level of lateral indention of head, equal to preorbital length, and 7.2% (7.3%) TL; head width at posterior edge of nostrils 1.4 and at mouth corners 1.8 (1.6) times width at level of lateral indention of head; head width at middle gill slits 1.6 times width at level of lateral indention of head. Snout long and slender, its tip broadly pointed, only slightly bell-shaped in dorsoventral view without distinct lateral indention; pre-outer nostril length 1.2 times internarial width and 0.5 times interorbital width; preoral length 0.7 times mouth width and 0.8 times preorbital length; preorbital length 3.1 (3.0) times in head length and equal to interorbital space. Eyes rather small and elongated, dorsolaterally on head, eye length 6.9 (6.0) times in head length, 15.3 (14.0) times in predorsal distance, and 1.8 (1.7) times eye height; nictitating lower eyelids, anterior and posterior eye notches, and suborbital groove present (Figures 6–7). Spiracles very small and subcircular, close behind but well separated from eyes, dorsolaterally on head and somewhat lower than level of eye notches, spiracle length 7.1 (6.0) times in eye length and 15.3 (12.2) times in interorbital width. Gill slits moderately long, well separated, gill filaments not visible externally, their upper ends clearly below lower edge of eye; first four gill openings subequal in height, the fifth shortest and above pectoral-fin origin. Nostrils oblique, expanding diagonally inwards from snout edge, clearly not reaching level of mouth, with triangular anterior nasal flaps; pre-outer nostril length subequal to nostril width and about half of preoral snout length, nostril width 1.1 times internarial width and about equal to eye length (Figures 6–7). Mouth broad, width 1.4 (1.3) times preoral length, 0.7 (0.8) times head width at mouth corners, 2.9 (2.6) times in head length, and twice mouth length.
Upper and lower labial furrows well developed, upper ones not reaching midpoint between mouth corner and posterior margin of nostril, lower furrows 1.5 (1.3) times as long as upper ones. Entire roof of mouth loosely set with elongated papillae of distinct size (Figure 8 A). Tongue moderately long, flat and rounded, light-colored, also loosely set with elongated oral papillae of distinct size (Figure 8 B). Fleshy buccal curtain along inner margin of upper jaw very densely set with large and globose papillae (Figures 8 C, D), fleshy curtain behind tooth rows in lower jaw loosely set with large and mostly furcated papillae (Figures 8 E, F).
......continued on the next page ......continued on the next page Upper jaw with 67 (76) rows and lower jaw with 64 (62) rows of small, tricuspidate teeth, median cusp much longer than lateral cusps (Figures 8 C, D); teeth of lower jaw similar to those of upper jaw (Figures 8 E, F). Cusps decrease in size from symphysis to mouth corners, whereas cusplet size increases, reducing the size difference of cusps and cusplets towards mouth corner. Outer surface of crown furrowed by strong longitudinal ridges from base of cusps and cusplets to tip. Cutting edges of cusps and cusplets without serrations.
Dermal denticles leaf-like to teardrop-shaped and overlapping on dorsal (Figure 9 A) and ventral (Figure 9 B) snout. Branchial dermal denticles tricuspidate with long and pointed median main cusp and shorter lateral cusplets at lower level, less densely set than on head (Figure 9 C). Lateral trunk denticles similar to branchial denticles, but more densely set (Figure 9 D). Dermal denticles on lateral caudal fin similar to those on trunk (Figure 9 E). Dermal denticles on anterior dorsal caudal-fin margin slightly enlarged, with very long median cusp and very short lateral cusplets and very densely set (Figure 9 F).
Pectoral fins subtriangular, non-falcate, anterior margin convex, its length 1.8 (1.7) times pectoral base length and subequal to the length of the straight posterior margin, apex rounded, inner margin convex and subequal to pectoral base length, inner pectoral corner broadly rounded (Figure 10 A). Pectoral-pelvic space 1.8 (1.5) times length of pectoral-fin anterior margin and 1.6 (1.5) times interdorsal space.
Pelvic fins narrowly triangular with long, straight anterior and posterior margins and shorter straight inner margin, anterior margin about half as long as pectoral-fin anterior margin; pelvic-fin origin clearly anterior to first dorsal-fin origin, pelvic posterior tips below insertion of first dorsal fin (Figure 10 B). Pelvic-anal space short, 10.2% (11.8%) TL and 0.6 (0.7) times pectoral-pelvic space.
First dorsal fin 1.4 (1.3) times higher than but about as long as second dorsal fin, anterior margin convex, apex rounded, posterior and inner margins straight, free rear tip angular; base length 1.3 (1.5) times fin height and about half of interdorsal space; first dorsal-fin origin over pelvic-fin midbase (Figure 10 B).
Second dorsal fin lower than first dorsal fin, anterior margin slightly convex, apex rounded, posterior and inner margins straight, free rear tip angular, base length 2.0 (2.4) times fin height and about half of interdorsal space; second dorsal-fin origin over anal-fin midbase (Figure 10 C).
Anal fin a long and low, uneven triangle, with long straight anterior margin, slightly shorter and weakly concave posterior margin, and short inner margin, apex rounded, free rear tip angular; base length 3.2 (3.9) times fin height and about equal to interdorsal and pelvic-anal spaces, respectively; base 1.7 times longer than second dorsal-fin base and 4.8 (16.9) times anal-caudal space (Figure 10 C). Anal-fin origin distinctly anterior to second dorsal-fin origin.
Caudal fin slender, moderately long and strongly asymmetrical, its length 4.9 (5.4) times fin height and 2.7 times the interdorsal space; dorsal caudal margin biconvex, mesially concave anterior to subterminal notch, no lateral undulations; upper caudal lobe very low, lower caudal lobe much deeper, with concave pre- and postventral margins of about equal length; ventral corner bluntly angled; subterminal notch distinct; terminal lobe about 4.2 (4.4) times in caudal-fin length; terminal caudal margin distinctly convex (Figure 10 D).
Claspers (Figure 11) rather short and thick, lateral margins nearly straight, not undulated, extending to about one third of their inner margin length beyond pelvic-fin free rear tips; inner margin length 9.1% TL, base width 2.1% TL. Glans moderately elongated, length about two thirds clasper inner margin; distally gradually tapering to pointed tip without knob-like apex. Ventral and outer lateral surfaces of clasper covered with small tricuspidate clasper denticles (CD), similar to those on trunk; dorsal and inner lateral surfaces largely naked. The narrow slitlike apopyle opens the clasper groove proximally; the hypopyle (HP) ends the concealed clasper groove distally and is detectable as a small cavity next to the rhipidion. The proximally concealed clasper groove (CG) opens widely in the distal glans. A large, fleshy flap, the envelope (EN), on outer lobe of glans, overlapping part of CG; outer lobe also with a large, subtriangular exorhipidion (ER), which consists of a proximal convex blade and a distal fleshy wall; few enlarged clasper denticles, the clasper hooks, along inner edge of ER. Inner lobe with a fanshaped flap, the rhipidion (RH), that partially covers the concealed part of CG and itself is partially concealed by a movable blade, the cover rhipidion (CR); inner lobe also with two blind cavities: the large and deep pseudopera (PP), that is partially concealed by EN and RH, and—on the inner margin—the longitudinally slit-like pseudosiphon.
Coloration. When fresh (paratype): rather distinct dark brown blotches at nape, dorsolaterally on body below first and second dorsal fins, and two across caudal fin; one large blotch on flank between pectoral and pelvic fin plus indistinct smaller ones along midlateral level between pectoral and second dorsal fin. Color in preservative (holotype and paratype): body anterior to cloaca bicolored with lateral demarcation of medium brown dorsal and whitish or beige ventral color, tail less distinctly bicolored with gradually fading brown color from dorsal to ventral side; about five indistinct darker blotches on dorsolateral surface at gill slits, below dorsal fins and at middle and posterior caudal fin (one additional blotch visible in the paratype between pectoral and pelvic fin); dark blotch above left pectoral fin in the holotype is an artefact of long-time storage with the fin adpressed to the body. Fins similar in color to body, but gradually brightening towards their margins; anal fin completely whitish or beige. Jaws, gums, and mouth cavity beige. Brauer (1908) described the coloration of the ‘Valdivia’ specimens as grayishbrown dorsally and brighter ventrally with several, 8–9, dark, broad but inconspicuous transverse bars on the back which do not reach the ventral body surface. However, his description probably only refers to one or both female specimens, which were deposited in the Museum of Natural History in Berlin (ZMB 17410 and ZMB 22423), where Brauer was employed. The assumption that his description did not include the holotype of the new species (ZMH 10163) is further supported by the differing remaining color pattern of the holotype which closely matches the pattern of the more recently caught paratype and by the fact that Brauer’s measurements only included specimen ZMB 22423.
Size. A very small catshark maturing at about 28 cm TL and probably attaining around 30 cm TL.
Distribution. Known from the upper slope off northern Tanzania in the Pemba Channel between Zanzibar and Pemba Island, 5° 27.9’ S, 39° 18.8’ E, in 463 m depth and from off southern Mozambique, 21°12'8" S, 35°41'8" E – 21°16'6" S, 35°41'3" E, in 490–550 m depth.
Etymology. The specific name tenuicephalus is derived from the remarkably narrow head and snout of the species (lat. tenuis = slender, cephalus = head).
Remarks. Bythaelurus tenuicephalus n. sp. is easily distinguished from its congeners based on the narrow shape of its head and snout, which is only slightly bell-shaped in dorsoventral view without distinct lateral indention. All other Bythaelurus species have distinctly bell-shaped heads with strong lateral indention anterior to outer nostrils.
The coloration of Bythaelurus tenuicephalus also clearly distinguishes it from B. clevai (Figure 12 A) due to having a color pattern of fewer and smaller blotches. Furthermore, B. tenuicephalus differs from B. clevai by attaining a smaller maximum size (about 30 cm TL vs. 39 cm TL according to Weigmann, in press), having larger papillae on tongue and especially roof of mouth, a smaller ratio eye length in predorsal space (14.0–15.3 vs. 16.7 times in the adult male ZMH 26071 of B. clevai), a smaller ratio pre-outer nostril length times internarial length (1.2 vs. 1.5), a shorter snout (preorbital length 6.7–7.1% TL vs. 8.3% TL, preoral length 5.5–5.7% vs. 7.0% TL), a shorter pectoral-pelvic space (16.4–16.6% TL vs. 19.7% TL), and broader claspers in adults (base width 2.1% TL vs. 1.8% TL). Additionally, the tip of the clasper does not have a knob-like apex (vs. tip with knob-like apex), the envelope is smaller, and the exorhipidion is subtriangular (vs. subrectangular).
Bythaelurus tenuicephalus is clearly distinct from B. hispidus (Figure 12 B) due to having a greater ratio preouter nostril length times internarial length (1.2 vs. 0.8 in adult male BMNH 1898.7.13.21 of B. hispidus), a longer snout (preorbital length 6.7–7.1% TL vs. 5.5% TL), a longer dorsal-caudal space (3.1–3.9% TL vs. 1.8% TL), a shorter pectoral-fin anterior margin length (9.3–10.8% TL vs. 12.1% TL), broader claspers in adults (base width 2.1% TL vs. 1.5% TL), less pointed dermal denticles on dorsal head, and more vertebral centra (monospondylous 38–40 vs. 37, diplospondylous precaudal 43–50 vs. 37, and total vertebral centra 133–138 vs. 122). Furthermore, the claspers in adults have a broad stem and proximal glans which distally rapidly tapers to the narrow tip (vs. claspers narrowly rod-like) and the tip of the clasper does not have a knob-like apex (vs. tip with knob-like apex).
The presence of large oral papillae on tongue and roof of mouth clearly distinguishes the new species from Bythaelurus lutarius (Figure 12 C), which is reported to have no papillae on tongue and roof. Although photographs of the holotype and one paratype of B. lutarius indicate that these specimens, in contrast to descriptions in the literature, do not completely lack oral papillae, they have extremely few and small papillae on tongue and roof, clearly different from the numerous large oral papillae in the new species. Further differences are a blotched (vs. largely plain) coloration, a smaller maximum size (about 30 cm TL vs. 39 cm TL following Weigmann, in press), a greater ratio pre-outer nostril length times internarial length (1.2 vs. 0.9 in the adult male holotype USNM 205135 of B. lutarius), shorter anterior nasal flaps (length 0.9–1.2% TL vs. 1.5% TL), a longer caudal fin (27.9–30.3% TL vs. 26.6% TL and 2.7 vs. 2.1 times interdorsal space), a shorter interdorsal space (10.4–11.1% TL vs. 12.7% TL), a shorter pelvic-anal space (10.2–11.8% TL vs. 13.6% TL and 0.6–0.7 vs. 0.9 times pectoral-pelvic space), and shorter and broader claspers in adults (outer margin length 5.8% TL vs. 8.0% TL, base width 2.1% TL vs. 1.5% TL).
A detailed comparison with Bythaelurus alcockii is not possible due to the unavailability of specimens or detailed descriptions. Based on Alcock’s (1899) description of the lost holotype of B. alcockii, B. tenuicephalus has a strongly different coloration (medium brown dorsally and whitish or beige ventrally with about five to six dark blotches on dorsolateral trunk and caudal fin vs. blackish with hoary gray surface and some fins white-tipped posteriorly), teeth with a long median main cusp and short lateral cusplets vs. teeth with cusps and cusplets of subequal length, and was caught in much shallower water (463–550 m vs. 1134–1262 m depth). The long snout and great catch depth—reported for B. alcockii by Alcock (1899) —indicate that this species possibly belongs to Apristurus rather than to Bythaelurus, like assumed by Compagno (1984a). However, the tooth morphology described for B. alcockii by Alcock (1899) does not fit the characters of neither Bythaelurus nor Apristurus species and therefore seems questionable. For the time being, B. alcockii remains a species of uncertain validity and generic assignment.
Generally, the deep-water catshark species of the genus Bythaelurus are mostly poorly known and more specimens are needed of several species, especially of those from the Indian Ocean. In order to further improve the knowledge of Bythaelurus species in the Indian Ocean, a comprehensive study on the taxonomy and distribution of B. hispidus and descriptions of further undescribed species of the genus from the western Indian Ocean are currently in preparation.
description: Published as part of Kaschner, Carina Julia, Weigmann, Simon & Thiel, Ralf, 2015, Bythaelurus tenuicephalus n. sp., a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the western Indian Ocean, pp. 120-138 in Zootaxa 4013 (1) on pages 121-136, DOI: 10.11646/zootaxa.4013.1.9, http://zenodo.org/record/242931