Bythaelurus bachi Weigmann, Ebert, Clerkin, Stehmann & Naylor, 2016, n. sp.
Creators: name: Weigmann, Simon
name: Ebert, David A.
name: Clerkin, Paul J.
name: Stehmann, Matthias F. W.
name: Naylor, Gavin J. P.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Elasmobranchii
Carcharhiniformes
Scyliorhinidae
Bythaelurus
Bythaelurus bachi

description: Bythaelurus bachi n. sp.
Bach’s Catshark
Figures 2–18; Tables 1–2
Holotype ZMH 26160, adult male, 422 mm TL fresh, 390.5 mm TL 70% ethanol preserved, RV ‘Vityaz’, cruise 17, station 2707, Walters Shoals, 33°01.8’ S, 44°23.6’ E – 32°59.8’ S, 44°24.4’ E, 910–925 m depth, 19.4 m shrimp trawl, trawl # 60, on the bottom for 60 minutes, 15 Dec 1988.
Paratypes (43) ZMH 26161, adult female with one egg case in each uterus, 405 mm TL fresh, 395 mm TL 70% ethanol preserved, RV ‘Vityaz’, cruise 17, station 2668, Walters Shoals, 33°01.2’ S, 44°36.8’ E – 33°05.2’ S, 44°39.2’ E, 1010 m depth, 19.4 m shrimp trawl, trawl # 48, on the bottom for 61 minutes, 0 8 Dec 1988; ZMH 26162, female post-embryo, 122 mm TL fresh, 120 mm TL 70% ethanol preserved, data the same as ZMH 26161; ZMH 26163, juvenile female, 227 mm TL fresh, 220 mm TL 70% ethanol preserved, data the same as ZMH 26161; ZMH 26164, juvenile female, 361 mm TL fresh, 355 mm TL 70% ethanol preserved, data the same as ZMH 26161; ZMH 26165, juvenile male, 210 mm TL fresh, 205 mm TL 70% ethanol preserved, data the same as ZMH 26161; ZMH 26166, juvenile male, 248 mm TL fresh, 240 mm TL 70% ethanol preserved, data the same as ZMH 26161; ZMH 26167, juvenile male, 253 mm TL fresh, 246 mm TL 70% ethanol preserved, data the same as ZMH 26161; ZMH 26168, juvenile male, 323 mm TL fresh, 317 mm TL 70% ethanol preserved, data the same as ZMH 26161; ZMH 26169, juvenile female, 290 mm TL fresh, 284 mm TL 70% ethanol preserved, RV ‘Vityaz’, cruise 17, station 2670, Walters Shoals, 33°01.6’ S, 44°49.2’ E – 33°04’ S, 44°49.1’ E, 1090–1100 m depth, 19.4 m shrimp trawl, trawl # 49, on the bottom for 60 minutes, 0 9 Dec 1988; ZMH 26170, juvenile female 292 mm TL fresh, 289 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26171, juvenile female 295 mm TL fresh, 290 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26172, juvenile female 314 mm TL fresh, 309 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26173, juvenile female 320 mm TL fresh, 312 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26174, juvenile female 339 mm TL fresh, 331 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26175, juvenile female 346 mm TL fresh, 339 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26176, juvenile female 350 mm TL fresh, 347 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26177, juvenile male 254 mm TL fresh, 248 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26178, juvenile male 305 mm TL fresh, 297 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26179, juvenile male 314 mm TL fresh, 309 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26180, juvenile male 322 mm TL fresh, 313 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26181, juvenile male 328 mm TL fresh, 322 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26182, juvenile male 354 mm TL fresh, 346 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26183, juvenile male 359 mm TL fresh, 349 mm TL 70% ethanol preserved, data the same as ZMH 26169; ZMH 26184, juvenile female, 312 mm TL fresh, 297 mm TL 70% ethanol preserved, RV ‘Vityaz’, cruise 17, station 2671, Walters Shoals, 32°56’ S, 45°01’ E – 32°59’ S, 45°03’ E, 1175–1200 m depth, 19.4 m shrimp trawl, trawl # 50, on the bottom for 60 minutes, 0 9 Dec 1988; ZMH 26185, female post-embryo, 144 mm TL fresh, 132 mm TL 70% ethanol preserved, RV ‘Vityaz’, cruise 17, station 2706, Walters Shoals, 33°01’ S, 44°30’ E – 33°05’ S, 44°32’ E, 970–980 m depth, 19.4 m shrimp trawl, trawl # 59, on the bottom for 40 minutes, 15 Dec 1988; ZMH 26186, juvenile male, 376 mm TL fresh, 350 mm TL 70% ethanol preserved, data the same as holotype ZMH 26160; ZMH 26187, adult male 410 mm TL fresh, 378 mm TL 70% ethanol preserved, data the same as holotype ZMH 26160; ZMH 26188, adult female, 404 mm TL fresh, 393 mm TL 70% ethanol preserved, RV ‘Vityaz’, cruise 17, station 2735, Walters Shoals, 33°36’ S, 44°32’ E – 33°38’ S, 44°34’ E, 930–950 m depth, 29 m shrimp trawl, trawl # 68, on the bottom for 75 minutes, 19 Dec 1988; ZMH 26189, adult female 407 mm TL fresh, 400 mm TL 70% ethanol preserved, data the same as ZMH 26188; ZMH 26190, female post-embryo, 132 mm TL fresh, 125 mm TL 70% ethanol preserved, data the same as ZMH 26188; ZMH 26191, juvenile female, 265 mm TL fresh, 245 mm TL 70% ethanol preserved, RV ‘Vityaz’, cruise 17, station 2736, Walters Shoals, 33°58.1’ S, 45°01’ E – 33°57’ S, 45°02.5’ E, 1030–1050 m depth, 29 m shrimp trawl, trawl # 69, on the bottom for 47 minutes, 19 Dec 1988; CAS 241442, 3 specimens: adult male, 400 mm TL (tissue accession GN 15514), adult females, 422 and 423 mm TL, Walters Shoals, 34°01’ S, 45°36’ E, 950–1340 m depth, bottom trawl, 16 May 2014; CAS 241443, pregnant female, 405 mm TL, Walters Shoals, 34°01’ S, 45°36’ E, 950–1345 m depth, bottom trawl, 14 Apr 2014; CAS 241444, 2 specimens: adult female, 392 mm TL (tissue accession GN 15516), adult female, 445 mm TL (tissue accession GN 15517), Walters Shoals, 34°01’ S, 45°36’ E, 960–1210 m depth, bottom trawl, 14 Apr 2014; CAS 241445 (tissue accession GN 12074), adult female, 404 mm TL, Walters Shoals, 34°24’ S, 45°06’ E, 1123–1294 m depth, bottom trawl, 4 May 2012; CAS 241478 (tissue accession GN 15515), pregnant female, 408 mm TL, Walters Shoals, 34°01’ S, 45°36’ E, 950–1365 m depth, bottom trawl, 16 May 2014; SAIAB 202736, adult female, 403 mm TL, data the same as CAS 241443; SAIAB 202737, adult female, 415 mm TL, data the same as CAS 241444; USNM 438923, adult female, 409 mm TL, data the same as CAS 241442; USNM 438924, adult female, 412 mm TL, data the same as CAS 241442.
Type specimens at ZMH were collected by M.F.W. Stehmann, those at CAS, SAIAB and USNM by P.J. Clerkin.
Diagnosis. A small scyliorhinid and a medium-sized Bythaelurus species with the following characteristics: body firm and stout (slender in juveniles); snout long (preorbital length 4.7–7.6% TL) and broad, bell-shaped in dorsoventral view with distinct lateral indention; pre-outer nostril length 1.1–1.9 times internarial space; preorbital snout length 0.7–1.0 times interorbital space; preoral snout length 1.0–1.9 times in mouth width; eye length 9.0– 13.0 times in predorsal distance, 3.6–5.4 times in head length and 1.4–4.1 times eye height; head length 1.8–2.7 times width at level of maximum outer extent of anterior nostrils; head width at level of maximum outer extent of anterior nostrils 1.1–1.5 times width at level of lateral indention of head, 1.1–1.8 times preorbital length, and 7.2– 10.0% TL; tongue and roof of mouth densely set with oral papillae of distinct size, which are partially very large and conglomerated from several single papillae; pelvic anterior margin 1.1–2.1 times in pectoral-fin anterior margin; first dorsal-fin base 1.0–1.8 times in interdorsal space; length of second dorsal-fin inner margin 0.5–1.9 times in second dorsal-fin height; second dorsal-fin base length 6.7–9.7% TL; anal-fin base 0.7–1.3 times interdorsal space. Coloration: body and fins plain beige to light grayish-brown, slightly brighter on ventral side. Upper jaw with 70–84 and lower jaw with 60–76 rows of small tri- to pentacuspidate teeth with outer surface of crown furrowed by strong longitudinal ridges and structured by reticulations in basal areas; monospondylous trunk vertebrae centra 38–43, diplospondylous precaudal centra 33–43, total centra 124–132. Dermal denticle morphology highly diverse in different body areas and post-embryonic specimens with very characteristic double row each of about 20 distinctly enlarged, blunt, spatulate, cross-based dermal denticles along dorsal trunk. Claspers rather long and very thick, inner margin length 10.6–11.3% TL, base width 2.3–3.1% TL; no clasper hooks, cover rhipidion and pseudosiphon very large, envelope elongated. The new species is easily distinguished from all congeners by the plain beige to light gray-brown coloration, high diversity in dermal denticle morphology, and presence of composite oral papillae. In the western Indian Ocean, it is the only stout-bodied species of Bythaelurus with oral papillae.
Description of the holotype (Figures 2–18). Values of the paratypes in parentheses. Morphometric measurements and meristics are given in Table 1.
External morphology. Body firm and stout (slender in juveniles), subcircular in cross section at mid-trunk, laterally compressed and tapering posterior to cloaca; head region broad, long abdominal and caudal sections (Figures 2–4). No predorsal, interdorsal, or postdorsal ridges; no postanal ridge; no lateral ridges on caudal peduncle. Trunk about as long as tail, distance from tip of snout to anterior cloaca 51.6% TL (42.0–53.2% TL, small values in post-embryos and small juveniles only, details can be found under Remarks); pre-first dorsal-fin length 50.1% TL (41.1–51.9% TL, small values in post-embryos and small juveniles only), pre-second dorsal-fin length 65.5% TL (56.4–66.7% TL, small values in post-embryos and small juveniles only), ventral precaudal length 71.7% TL (61.7–72.8% TL, small values in post-embryos and small juveniles only). Head broad and dorsoventrally flattened, with a broadly rounded snout; laterally slightly compressed in gill region (Figure 5); no supraorbital crests on chondrocranium; head length 2.6 (1.8–2.7) times width at level of maximum extent of anterior nostrils and 1.0 (0.6–1.3) times pectoral—pelvic space; head width at level of maximum outer extent of anterior nostrils 1.3 (1.1–1.5) times width at level of lateral indention of head, 1.3 (1.1–1.8) times preorbital length, and 8.8% (7.2–10.0%) TL; head width at posterior edge of nostrils 1.6 (1.2–1.7) and at mouth corners 2.0 (1.5–2.2) times width at level of lateral indention of head; head width at middle gill slits 1.8 (1.2–2.1) times width at level of lateral indention of head. Snout long and broad, its tip broadly rounded, strongly bell-shaped in dorsoventral view with distinct lateral indention; pre-outer nostril length 1.5 (1.1–1.9) times internarial width and 0.5 (0.4–0.8) times interorbital width; preoral length 0.8 (0.5–1.1) times mouth width and 1.1 (0.8–1.5) times preorbital length; preorbital length 3.5 (2.4–4.1) times in head length and 0.8 (0.7–1.0) times interorbital space. Eyes rather large and elongated, dorsolaterally on head, eye length 4.7 (3.6–5.4) times in head length, 10.3 (9.0–13.0) times in predorsal distance, and 2.1 (1.4–4.1) times eye height; nictitating lower eyelids, anterior and posterior eye notches, and suborbital grooves present. Spiracles very small and slit-like, close behind but well separated from eyes, dorsolaterally on head and somewhat lower than level of eye notches, spiracle length 9.0 (6.2–14.5) times in eye length and 14.7 (10.2–25.2) times in interorbital width. Gill slits moderately long, well separated, their upper ends clearly below level of lower edge of eye; gill area fully scaled, gill filaments not visible externally; gill openings decreasing in size from first to fifth, the latter 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 1.0 (0.7–2.1) times nostril width and 0.5 (0.5–0.9) times preoral snout length, nostril width 1.6 (0.8–1.9) times internarial width and 0.8 (0.5–1.0) times eye length. Mouth broad, width 1.3 (1.0–1.9) times preoral length, 0.6 (0.5–0.8) times head width at mouth corners, 2.6 (2.0–3.4) times in head length, and 2.8 (1.6–3.6) times mouth length. Upper and lower labial furrows well developed, upper ones not reaching midpoint between mouth corner and posterior margin of nostril, lower furrows 1.4 (1.1–2.8) times as long as upper ones. Tongue moderately long, flat and rounded, light-colored, densely set with oral papillae of distinct size (Figure 6 A–B). Entire roof of mouth also densely set with papillae of distinct size, which are partially very large and conglomerated from several single papillae (Figure 6 C–F; Figure 7). Fleshy buccal curtain along inner margin of upper and lower jaws densely set with large and globose papillae (Figure 7).
......continued on the next page Upper jaw with approximately 84 (70–84) and lower jaw with about 74 (60–76) diagonal rows of small teeth (n = 14; Figure 7). Anterolateral teeth in upper jaw tricuspidate (partially with minute additional cusplets) with median cusp much longer than lateral cusps (Figure 8 A–B); posterolateral teeth in upper jaw tetra- to pentacuspidate and with median cusp only slightly longer than lateral cusps (Figure 8 C–D). Anterolateral (Figure 8 E–F) and posterolateral (Figure 8 G–H) teeth in lower jaw similar to posterolateral teeth in upper jaw. Outer surface of crown furrowed by strong longitudinal ridges from base of cusps to tip and structured by reticulations in basal areas. Cutting edges of cusps without serrations.
Dermal denticles densely set and strongly overlapping. Dermal denticles on dorsal snout tip leaf-like, surface almost completely structured by reticulations, median ridge very narrow and reaching denticle tip (Figure 9 A–B).
Dermal denticles on ventral snout tip subrhombic, surface structured by reticulations only in basal two thirds, median ridge very narrow and not reaching denticle tip (Figure 9 C–D). Branchial dermal denticles tricuspidate with long, pointed and broad median cusp and tiny lateral cusps at lower level, surface structured by reticulations in basal two thirds, one or two median ridges that do not fuse and do not reach the tip of the median cusp (Figure 9 E– F). Lateral trunk denticles tricuspidate with long, pointed and slender median cusp and small lateral cusps at lower level, surface almost completely structured by reticulations, two median ridges that fuse near the tip of the median cusp and reach the tip (Figure 10 A–B). Dermal denticles on lateral caudal fin similar, tricuspidate with long, pointed and slender median cusp and tiny lateral cusps at lower level, surface almost completely structured by fine reticulations, two median ridges that fuse near the tip of the median cusp and reach its tip (Figure 10 C–D). Dermal denticles on anterior dorsal caudal-fin margin slightly enlarged, with short median cusp and slightly shorter lateral cusps, surface structured by reticulations in basal half, one or two median and two to four lateral ridges, the median ridges rarely fuse near the tip of the median cusp and only one median ridge reaches the tip, the lateral ridges do not fuse and only one reaches the tip of each lateral cusp (Figure 10 E–F). Post-embryonic paratypes (ZMH 26162, ZMH 26185, and ZMH 26190) with very characteristic double row of each about 20 distinctly enlarged, blunt, spatulate, cross-based dermal denticles along dorsal trunk from about level origin of pectoral fins to slightly posterior to origin of first dorsal fin (Figure 11; Figure 12 A–C). The body is otherwise loosely set with nonoverlapping, small, needle-shaped dermal denticles (Figure 12 B–D).
Pectoral fins subtriangular, non-falcate, anterior margin weakly convex, its length 1.9 (1.4–2.2) times pectoral base length and 1.1 (1.0–2.1) times length of the weakly convex posterior margin, apex rounded, inner margin convex and 1.2 (0.6–1.3) times pectoral base length, inner pectoral corner broadly rounded (Figure 5). Pectoral - pelvic space 2.1 (1.3–3.0) times length of pectoral-fin anterior margin and 2.5 (1.5–3.2) times interdorsal space.
Pelvic fins narrowly triangular with long, straight anterior and posterior margins and shorter straight inner margin, anterior margin 0.8 (0.5–0.9) times pectoral-fin anterior margin, apex very bluntly rounded; pelvic-fin origin clearly anterior to first dorsal-fin origin, pelvic posterior tips behind level of insertion of first dorsal fin (Figure 13 A). Pelvic—anal space very short, 6.7% (3.0–8.6%) TL and 0.3 (0.1–0.4) times pectoral—pelvic space.
First dorsal fin 0.8 (0.8–1.2) times as high and 1.0 (0.8–1.0) times as long as second dorsal fin, anterior margin convex, apex rounded, posterior and inner margins straight, free rear tip rounded; base length 1.9 (1.2–2.8) times fin height and 0.9 (0.5–1.0) times interdorsal space; first dorsal-fin origin anterior to level of pelvic-fin midbase (Figure 13 A).
Second dorsal fin slightly higher (slightly higher to slightly lower) than first dorsal fin, anterior margin slightly convex, apex rounded, posterior and inner margins straight, free rear tip rounded, base length 1.7 (1.3–3.9: 3.0– 3.9 in post-embryos ZMH 26162 and ZMH 26185, 1.3–2.2 in all other paratypes) times fin height and 0.9 (0.6–1.2) times interdorsal space; second dorsal-fin origin over anal-fin midbase (Figure 13 A).
Anal fin a long and high, uneven triangle, with long straight anterior margin, slightly shorter and straight posterior margin, and short inner margin, apex rounded, free rear tip pointed angular; base length 1.8 (1.4–2.9) times fin height, 1.2 (0.7–1.3) times interdorsal space, and 1.5 (1.0–3.1) times pelvic—anal space; base 1.2 (1.0– 1.5) times longer than second dorsal-fin base. Anal—caudal space absent (absent to 1.6% TL) (Figure 13 A). Analfin origin distinctly anterior to second dorsal-fin origin.
Caudal fin slender, moderately long and strongly asymmetrical, its length 4.3 (3.7–6.5) times fin height and 3.3 (2.4–4.3) times interdorsal space; dorsal caudal margin weakly convex, no lateral undulations; upper caudal lobe very low, lower caudal lobe much deeper, with straight pre- and postventral margins. Ventral caudal-fin origin far anterior of dorsal caudal-fin origin due to very long preventral margin, which is slightly longer than the postventral margin and forms a strongly elongated fleshy ridge in about anterior two-thirds of its length. Ventral corner bluntly angled; subterminal notch distinct; terminal lobe 5.0 (4.1–6.5) times in caudal fin length; terminal caudal margin nearly straight with mesial indention (Figure 13 B).
Claspers (Figure 14) rather long, overlapping anal-fin origin, and very broad, 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 11.0% (10.6–11.3%) TL, base width 2.5% (2.3–3.1%) TL. Glans somewhat elongated, length about half clasper inner margin; only slightly tapering to tip in distal half but terminally abruptly narrowing to bluntly 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 ends the concealed clasper groove distally and is detectable as a small cavity next to the rhipidion, but both are concealed by the cover rhipidion and exorhipidion and thus not visible in Figure 14. The proximally concealed clasper groove (CG) opens widely in the distal glans. An elongated, fleshy flap, the envelope (EN), on outer lobe of glans, does not overlap part of CG; outer lobe also with a large, subtriangular exorhipidion (ER), which consists of a proximal convex blade and a distal fleshy wall; no enlarged clasper denticles (clasper hooks) along inner edge of ER. Inner lobe with a fan-shaped flap, the rhipidion, that partially covers the concealed part of CG and itself is concealed by a movable blade, the large 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 large, longitudinally slit-like pseudosiphon (PS).
Egg cases (Figure 15): the reproductive mode was determined to be oviparous based on egg cases found in adult female paratypes ZMH 26161, CAS 241443 and CAS 241478. Each female had a single fully developed egg case per uterus. The egg cases are small, 62.6–69 mm long, excluding horns, relatively broad, and thick, maximum anterior case width about 28.3–31.7% of case length, maximum posterior case width about 32.6–40.2% of case length, and minimum case width (through indention) about 24.6–30.9% of case length; greatest case height about 16.8–18.1% of case length and about 44.1–55.6% of posterior case width. Egg case surface with very fine striations, relatively smooth to the touch. Lateral keels of case narrow, about 1 mm wide, flat, and without T-shaped lateral surface, extending along entire capsule length and continuous with horns at both ends. The anterior border of case is narrow and concave, with horns narrow, very short, and curved inwards, overlapping slightly, and without any evidence of tendrils being present. The posterior border of case is slightly concave, broad, and with horns relatively long, also without any evidence of tendrils being present. Posterior apron short, length about 15% of case length, and wide, with weakly concave transverse edge, and attached to horns over about 3/4 of horn length, the tips of which are only free and curving inward. Anterior horns somewhat longer than posterior ones, curved inward over their entire length and with their tips nearing to each other much closer than tips of posterior horns. Anterior apron short, length about 10% of case length, and appearing strongly folded longitudinally, with folds almost ridge-like, and extending to tips of horns. The egg cases removed from the preserved females were light brown with a greenish tinge.
Skeletal meristics (from radiographs, n = 28, Table 1): monospondylous trunk vertebral centra: 40 (38–43); diplospondylous precaudal centra: 38 (33–43); total precaudal centra: 78 (73–83); caudal centra: 54 (48–56); total centra: 132 (124–132). Spiral valve turns (counted in three partially dissected paratypes): 6–8.
Coloration. Fresh, prior to preservation: nearly plain colored without pattern; back, upper flanks and fins light grayish-brown, becoming lighter to creamy white or light grayish on body and ventral body creamy; prenasal area and caudal peduncle brownish; all fins with very narrow dusky edging of anterior margins; dorsal fins with very narrow pale posterior edge (Figure 16). Post-embryonic specimens have a distinctly dark edge along margins of dorsal, pelvic, anal, and especially caudal fins (Figure 17). Color in preservative: body and fins plain beige to light grayish-brown, slightly brighter on ventral side (Figures 3–4). Dark fin edges of post-embryonic specimens are still prominent in specimen ZMH 26162 (Figure 11) but specimens ZMH 26185 and ZMH 26190 have almost completely faded. All specimens from station 2670 (ZMH 26169–26183) have almost completely faded as well. Furthermore, the latter specimens have become very fragile and partially damaged.
Molecular analyses (Figure 18). The maximum likelihood analysis of the aligned NADH2 sequence data clearly shows that Bythaelurus bachi is a monophyletic lineage that is distinct from, but closely related to, B. naylori. These two species fall as sister to B. dawsoni (Springer, 1971) from New Zealand. Representatives of B. canescens (Günther, 1878) and B. hispidus were included in the analysis for comparitive purposes. Both fall outside the clade containing B. bachi, B. naylori and B. dawsoni. It is important that not too much stock be placed in the phylogenetic arrangements presented as the inference is based on a single mitochondrial gene and because the sampling of taxa is sparse. Several described species of Bythaelurus and closely related genera were not included in the present analysis because fresh tissue samples were not available. We anticipate a more comprehensive analysis of the group at a later date as and when tissues become available.
Size (based on total length measurements prior to preservation). A small catshark and a medium-sized species of Bythaelurus reaching a maximum total length of about 445 mm for females and 422 mm for males. Females are mature at 392 mm and immature at 361 mm, males are mature at 400 mm and immature at 376 mm. Size at hatching based on the three post-embryonic specimens is estimated at around 120 mm TL.
Distribution. Known only from the southern end of the Madagascar Ridge at Walters Shoals in 910–1365 m depth (Figure 1).
Etymology. The new species is named in honor of Johann Sebastian Bach (1685–1750), a musical genius and one of the greatest composers of all time.
Remarks. There are several morphometric differences between the post-embryonic, small immature, and large immature plus adult specimens of Bythaelurus bachi, which might be of ontogenetic nature. These differences are demonstrated in Table 2.
As indicated in Table 2, there is strong variation in the measurements of pectoral—pelvic space among specimens> 250 mm TL, which ranges from 20.2 to 26.0% TL in the holotype and 22 paratypes of 284–400 mm TL in the ZMH collection and from 26.6 to 31.6% TL in the 12 other paratypes of 392–445 mm TL. Due to the geographic proximity of catch locations and individual differences in taking the measurement having been excluded, the large pectoral—pelvic space might be a characteristic of very large specimens. Nevertheless, this difference might also be influenced by the condition of the specimens.
description: Published as part of Weigmann, Simon, Ebert, David A., Clerkin, Paul J., Stehmann, Matthias F. W. & Naylor, Gavin J. P., 2016, Bythaelurus bachi n. sp., a new deep-water catshark (Carcharhiniformes, Scyliorhinidae) from the southwestern Indian Ocean, with a review of Bythaelurus species and a key to their identification, pp. 401-432 in Zootaxa 4208 (5) on pages 403-421, DOI: 10.11646/zootaxa.4208.5.1, http://zenodo.org/record/211686