Bythaelurus giddingsi E, Long & Baldwin, 2012, sp. nov.
Creators: name: E, John
name: Long, Douglas J.
name: Baldwin, Carole C.
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Elasmobranchii
Carcharhiniformes
Scyliorhinidae
Bythaelurus
Bythaelurus giddingsi

description: Bythaelurus giddingsi sp. nov.
(Figures 1–4, Plates 1–2, Tables 1–2)
Proposed common name. Galápagos Catshark.
Bythaelurus sp.: Compagno (2005b: 20), McCosker & Rosenblatt (2010: 172, 187), Ruiz et al., (2011: 12).
Bythaelurus sp. B: Compagno et al. (2005: 215, pl. 35), Kyne & Simpendorfer (2007: 53), Hearn et al. (2009: 51).
Material examined. All specimens are from the Galápagos Islands, collected aboard the submersible Johnson Sea- Link during 1995 and 1998.
Holotype. CAS 210091, 402 mm TL, female, Darwin Island, 0 1o 42.0' N, 92o00.0' W, (station number JSL 3103, field number JM 145), 428 m depth, collected by J.E. McCosker on 18 July 1998.
Paratypes. MNHN 2010-0004 (originally CAS 210092), 324 mm TL, immature male, JM 146; SIO 99-99, 217 mm TL, immature male, JM 147; and CAS 210093, 300 mm TL (partially dissected), immature female, JM 148; Darwin Island, all collected with the holotype. CAS 86559, 261 mm, immature male, Darwin Island, 0 1o 42.05' N, 92o00.02' W (JSL 3967), 511 m depth, collected by J.E. McCosker on 21 Nov. 1995. USNM 364283, 301 mm TL, immature female, Marchena Island, N. shore, 0 0o 24.0' N, 90o26.5' W (JSL 3106, JM 175 & CB 98-49), 562 m depth, collected by C.C. Baldwin on 19 July 1998. SAM- 35042, 453 mm TL, male, Marchena Island, N. shore, 0 0o 24.0' N, 90o26.5' W (JSL 3109, JM 199), 454 m depth, collected by J.E. McCosker on 21 July 1998.
Diagnosis. A moderate-sized species of Bythaelurus with the following characteristics: snout bluntly rounded; preoral length 4.7–6.8% TL; head short, its length about equal to pectoral-pelvic space, 21–24% TL; precaudal length 73–80% TL; dorsal and anal fins subequal; length of anal-fin base about equal to length of interdorsal space; precaudal vertebrae 81–85 (mean = 82.6); color chocolate brown dorsally, paler on ventral surface from snout to anus; body, flanks, caudal and median fins overlain with pale spots about equal in size to eye, becoming smaller below lateral midline, and showing a bilaterally asymmetrical pattern.
Description. Measurements are in millimeters, parenthetically followed by their proportions as percentages of total length and precaudal length, respectively. Proportions and counts of the holotype and paratypes are listed in Tables 1–2.
continued next page Total length 402 (100, 124); precaudal length 323 (80.3, 100). Tip of snout to: upper symphysis 41 (10.2, 12.7); nostrils 18.3 (4.6, 5.7); orbits 24 (6.0, 7.4); spiracles 48 (11.9, 14.9); 1st gill openings 70 (17.4, 21.7); 2nd gill openings 82 (20.3, 25.4); 3rd gill openings 89 (22.1, 27.6); 4th gill openings 92 (22.9, 28.5); 5th gill openings (= head length) 96.5 (24.0, 29.9); pectoral origins 90 (22.4, 27.9); pelvic origins 190 (47.3, 58.9); 1st dorsal origin 187 (46.5, 57.9); 2nd dorsal origin 259 (64.4, 80.2); anal origin 239 (59.5, 74.0); vent 194 (48.3, 60.1). Distance between: vent and caudal-fin tip 208 (51.7, 64.4); 1st and 2nd dorsal origins 72 (17.9, 22.3); 1st and 2nd dorsal bases 43 (10.7, 13.3); 2nd dorsal and upper caudal origins 53.5 (13.3, 16.7); 2nd dorsal base and upper caudal origin 24.5 (60.9, 75.9); pectoral and pelvic origins 100 (24.9, 31.0); pelvic and anal bases 23.5 (58.6, 72.8); anal and lower caudal origins 70 (17.4, 21.7); anal base and lower caudal origin 32 (80.0, 99.1). Eyes (palpebral apertures or fleshy orbits): length 20 (5.0, 6.2); height 7 (1.7, 2.2); width across anterior corners (interorbital) 34 (8.5, 10.5); eyeball diameter 8.5 (2.1, 2.6). Nostril width 12 (3.0, 3.7); internarial space 10 (2.5, 3.1). Spiracles: diameter 4 (1.0, 1.2); space between spiracles and eyes 3.3 (0.8, 1.0). Mouth (jaws in retracted position): length 21.5 (5.4, 6.6); width 46 (11.4, 14.2); width across outer edges of jaws 52 (12.9, 16.1). Gill-opening heights: 1st 12 (3.0, 3.7); 2nd 11(2.7, 3.4); 3rd 11 (2.7, 3.4); 4th 11 (2.7, 3.4); 5th 10 (2.5, 3.1). Head height: at spiracles 35 (8.7, 10.8); at 1st gill openings 43 (10.7, 13.3); at 5th gill openings 53 (13.2, 16.4). Trunk height: at 1st dorsal origin 51 (12.7, 15.8); at pelvic origins 41.5 (10.3, 12.8); at pelvic insertions 24 (6.0, 7.4). Girth: at 1st dorsal origin 125 (31.1, 38.7); at 2nd dorsal origin 57 (14.2, 17.6). Caudal peduncle height: at 2nd dorsal insertion 17 (4.2, 5.3); at upper caudal origin 13 (3.2, 4.0). Caudal peduncle width: at 2nd dorsal insertion 10.5 (2.6, 3.3); at upper caudal origin 7 (1.7, 2.2). Pectoral fin (right side - left is damaged), length of: anterior margin 50 (12.4, 15.5); posterior margin 45 (11.2, 13.9); origin to free rear tip 35 (8.5, 10.8); inner margin 30.5 (7.6, 9.4). Pelvic fins, length of: anterior margin 26.5 (6.6, 8.3); posterior margin 28.5 (7.1, 8.8); base 29 (7.2, 9.0); origin to free rear tip 40 (10.0, 12.4); inner margin 19.5 (4.9, 6.0); height 18 (4.5, 5.6). 1st dorsal fin, length of: anterior margin 37.5 (9.3, 11.6); posterior margin 24 (6.0, 7.4); base 28 (7.0, 8.7); inner margin 10 (2.5, 3.1); height 27 (6.7, 8.4). 2nd dorsal fin, length of: anterior margin 41 (10.2, 12.7); posterior margin 24 (6.0, 7.4); base 29 (7.2, 9.0); inner margin 10 (2.5, 3.1); height 26 (6.5, 8.0). Anal fin, length of: anterior margin 31 (7.7, 9.6); posterior margin 31 (7.7, 9.6); base 32 (8.8, 9.0); inner margin 8.5 (2.1, 2.6); height 21 (5.2, 6.5). Caudal fin, length of: dorsal margin 93 (23.1, 28.8); preventral margin 28 (7.0, 8.7); upper and lower postventral margins (combined) 47 (11.7, 14.6); subterminal margin 18.5 (4.6, 5.7); terminal margin 23 (5.7, 7.1); terminal lobe or sector 26 (6.5, 8.0); width of dorsal lobe at postventral notch 8 (2.0, 2.5); width of ventral lobe at postventral notch 2.5 (0.6, 0.8). Vertebral counts are given in Table 2.
Snout bluntly rounded, without a pointed knoblike tip (Figure 2, Plate 1). Head short, its length about equal to pectoral-pelvic space. Head depressed, roughly trapezoidal in cross-section. Outline of head in lateral view convex dorsally. Preoral snout short, nearly 1/2 mouth width, broadly rounded in dorsolateral view, minimally indented anterior to nostrils.
External eye openings with prominent anterior and posterior eye notches; eyes moderate and spindle-shaped; eye length 4.0– 5.5 in head length and 3.0–4.8 times eye height. Eyes dorsolaterally on head, slightly above lateral midline. Subocular ledge broad and strong. Nictitating lower eyelids rudimentary, with shallow subocular pouches.
Spiracles minute, length 3.8–7.6 in eye length, 0.2–0.3 eye lengths behind and below the posterior eye notch. First four gill openings longer than the fifth. Upper edge of each gill opening below eye and spiracle. Gill openings nearly straight, gill filaments not visible from outside. A few minute gill-raker papillae present on gill arches.
Nostrils with broad, angular nasal flaps with rounded tips and moderate mesonarial flaps lateral on anterior nasal flaps, moderate excurrent apertures, no posterior nasal flaps. Nostrils nearly reaching level of mouth. Mouth broadly angular, short, its width 1.6–2.5 in head length. Mouth length 2.0– 3.2 in mouth width. Lower symphysis nearly reaching upper symphysis. Maxillary teeth visible in ventral view (refer to Plate 1 for above characters). Tongue moderate, flat and rounded, filling most of floor of mouth. Many small buccal papillae on tongue and palate.
Teeth in 20–23/23–26 rows; 3–5/4–6 series functional, with more series functional in larger specimens and in posterior tooth rows than anterolaterals. Posterolateral teeth not arranged in diagonal files. No toothless spaces at symphysis. Teeth not strongly differentiated within jaws, but tooth-row groups along jaws demonstrating weakly defined monognathic heterodonty including symphyseals (S), anterior (A), anterolaterals (AL), and posteriors (P) in both jaws. No apparent difference in dentition between genders.
Anterolateral teeth (Figure 3) consist of single principal cusp with two pairs of lateral cusplets. Labial face of crown foot moderately concave, lingual face moderately convex. Principal cusp usually erect or showing slight distal inclination; this cusp mildly constricted at base at main crown, expanding slightly apically, tapering to an acute apex. Labial and lingual faces of cusp and cusplets mildly convex with short apicobasal ridges extending from crown foot to about 10% or less of height of principal cusp and cusplets. Primary cusplets, those proximal to principal cusp, erect or curving slightly toward central cusp, primary cusplets approximately 50% of height of central cusp; secondary cusplets, those distal to principal cusp, approximately 10–20% of height of primary cusp. A thin, unserrated cutting edge present on medial and distal edges of primary cusp and lateral cusplets, beginning at crown foot and terminating near crown apices. In posterior teeth, relative height of principal cusp reduced, cusp becoming comparatively wider, and relative height of cusplets increasing but never exceeding height of principal cusp. Symphyseal teeth with relatively narrow and usually containing only one pair of lateral cusplets. Lower teeth similar overall to anterolateral teeth except primary cusplets 60–90% length of principal cusp in anterolateral teeth.
Body robust in head and trunk region, nearly circular in cross section at mid-trunk, laterally compressed and tapering posterior to anus. No predorsal, interdorsal, or postdorsal ridges on midline of back; no postanal ridge between anal-fin base and lower caudal-fin origin. Lateral ridges absent from body. Caudal peduncle moderately elongate, laterally compressed, without lateral keels. Caudal-peduncle height 1.7–2.4 its width at posterior insertion of second dorsal fin, 1.3–2.3 in dorsocaudal space.
Dermal denticles, based on an examination of the holotype, vary widely in morphology depending on location on body (Plate 2). Dorsal dermal denticles, from dorsal surface of head and on trunk above lateral line, embedded in skin, spaced apart from (and not overlapping with) one another; these denticles blunt and single-cusped, widest at anterior base, often with two anterolateral lobes, and with 4–8 short, blunt longitudinal keels at base, often with keels extending posteriorly along most of length of denticles and becoming weaker near posterior apex. Lateral sides of the denticles usually weakly concave or occasionally straight; posterior apex acutely pointed, often rising well above skin giving a bristly appearance to dorsal surface of the head and body. Denticles longer than wide, those on dorsal trunk 2–3 times larger, more elongated, and with a more acute posterior apex than those on head. Dorsal dermal denticles, the only pigmented denticles on body, with pigment embedded in their anterior bases. Dermal denticles on lateral flanks colorless and semi-transparent, widely convex centrally and abruptly tapering to a thin, acute posterior apex; denticles longer than wide, with widest point at middle, usually smooth or showing a very weak central keel in middle, that keel absent at anterior base and posterior apex. Denticles are closely spaced and usually not overlapping, but sometimes barely so. Ventral dermal denticles colorless and semi-transparent, very thin without longitudinal keels; denticles wider than long, widest at base, quickly tapering to a blunt posterior apex; some denticles with a very short groove at medial base. Ventral dermal denticles closely-packed, usually with lateral edges barely overlapping neighboring denticles.
Dorsal edge of caudal fin, from caudal pit to posterior fin edge and from lateral line to the dorsal edge, with clumped comb-like dermal denticles that together exhibit the file-like “caudal crest” characteristic seen in several other Bythaelurus and Parmaturus catshark species (Springer 1979). These denticles transparent, elevated well above skin, and usually overlap 10–50% atop neighboring denticles. Each denticle consists of a single sharplypointed primary cusp with two (rarely one) large lateral secondary cusplets only nominally shorter than primary cusp; each cusp with a single longitudinal keel extending from anterior base to posterior apex. Denticles somewhat longer than wide, with widely convex lateral margins, the widest point at middle of denticle where lateral cusplets diverge from main body. Denticles on caudal fin below lateral line transparent, lanceolate and basally widest, tapering posteriorly, with straight or weakly convex lateral edges and a bluntly pointed posterior apex. These denticles flat and thin, without lateral cusplets and longitudinal keels, but exhibiting a short central grove at anterior base. Denticles on caudal fin below lateral line slightly elevated above skin and are closely spaced, but not touching or overlapping. In comparing denticle morphology and arrangement between holotype and paratypes, denticles vary little between largest and smallest specimens and between males and females. Relative size of dorsal denticles on head and body of smaller specimens longer, giving them more of a bristly appearance (Plate 1, Figure 4), an ontogenetic trait noted by Shouthall & Sims (2003) in the catshark Scyliorhinus canicula.
Pectoral fins triangular, broad and rounded, not falcate, with broadly convex anterior margins, narrowly rounded apices, broadly rounded posterior margins, and free rear tips, inner margins and narrow bases. Pectoral-fin area subequal to area of first dorsal fin. Origins of pectoral fins beneath interspace between third and fourth gill openings. Apex of pectoral fin slightly anterior to its free rear tip when fin is elevated and appressed to body.
Pelvic fins broadly triangular. Pelvic anterior margins 1.2–2.4 in pectoral fin anterior margins. Pelvic area subequal to anal-fin area. Pelvic-fin anterior margins slightly curved, apices narrowly rounded, posterior margins nearly straight, free rear tips narrowly rounded, inner margins straight and not fused together over claspers of juvenile males.
First dorsal fin high, apically narrow and not falcate, with nearly straight anterior margin, narrowly rounded apex, slightly convex posterior margin, angular free rear tip, and straight inner margin. First dorsal-fin origin over middle of pelvic-fin base, insertion of fin just above a line behind insertion of pelvic fin. First dorsal-fin base 1.5– 2.5 in interdorsal space, first dorsal-fin height 0.7–1.2 in first dorsal-fin base.
Second dorsal fin high, apically narrow and not falcate, subequal to first dorsal-fin in area and about subequal to first dorsal-fin height and base. Second dorsal fin with nearly straight anterior margin, narrowly rounded apex, slightly convex posterior margin, angular free rear tip, and straight inner margin. Second dorsal-fin origin in a line above anal-fin midbase, its insertion above anal-fin free rear tip, and free rear tip in front of upper caudal-fin origin by the length of its base. Second dorsal-fin base 0.6–0.9 in dorsocaudal space, second dorsal-fin height 1.1–1.5 in second dorsal-fin base, second dorsal fin inner margin 1.5–2.6 in second dorsal-fin height and 1.9–2.9 in second dorsal-fin base.
Anal fin low, apically broad, not falcate, about equal in size, height and base to that of second dorsal fin. Anterior margin slightly concave, apex broadly rounded, free rear tip bluntly pointed, and inner margin nearly straight. Anal-fin base without preanal ridges, anal-fin origin about 0.7–1.1 times anal-fin base length behind pelvic-fin insertions. Anal-fin posterior margin slanting posterodorsally, anal-fin insertion posterior to apex. Anal-fin base 0.8–1.4 in anal-caudal space, anal-fin height 1.5–2.0 in anal-fin base.
PLATE 1. Dorsal and ventral views of three specimens of Bythaelurus giddingsi sp. nov. showing relative variation in the shape of the nasal flaps, the mouth, upper dentition, and dermal denticles on dorsum of head. Left: Holotype CAS 210091, adult female, 402 mm TL. Center: Paratype USNM 364283, immature female, 301 mm TL. Right: Paratype CAS 86559, immature male, 261 mm TL.
Caudal fin narrow and asymmetrical, with large terminal lobe but ventral lobe not developed. Caudal fin short, dorsal margin 0.2–0.3 in precaudal length. Preventral caudal-fin margin 1.9–3.4 in dorsal caudal-fin margin, terminal lobe 3.0– 3.7 in dorsal caudal-fin margin. Dorsal caudal-fin margin without lateral undulations but proximally and distally convex with a shallow concavity between the convexities. Preventral caudal-fin margin basally concave and apically straight, tip of ventral caudal-fin lobe bluntly rounded. Postventral margin not differentiated into upper and lower parts, its margin straight to concave. Subterminal notch a narrow slot, subterminal margin straight to concave and terminal margin straight and sometimes notched. Lobe formed by these margins slightly angular, tip of tail broadly rounded.
Vertebral counts and statistics are given in Table 2. The precise number of caudal centra difficult to identify due to their small size and abundance of large caudal denticles; therefore counts of both the number of caudal centra and total number of centra are approximate. Transition between MP and DP centra about 4–6 centra behind front of pelvic girdle. Last few MP centra before MP-DP transition hardly enlarged, not forming a "stutter zone" of alternating long and short centra. Dimensions (in mm) of selected centra of holotype: length of penultimate MP 4.02; width of penultimate MP 3.02; midcentral width of penultimate centrum 0.94; length of first PD 2.75; width of first PD 3.08; midcentral width of first PD 1.14. "A ratio" (Springer & Garrick, 1964) of holotype 146. "B ratio" (Springer & Garrick, 1964) of holotype 133. Ratio of DP/MP of holotype 1.0.
Color. In ethanol, chocolate brown dorsally, becoming pale brown on ventral surface from snout to anus. Body and flanks overlain with pale spots the largest of which about equal in size to eye, becoming smaller below lateral midline. A pale spot at anterior base of each dorsal fin. Pale spots extending onto caudal and median fins. Caudal region and all fins chocolate brown. The posterior margin of paired and dorsal fins pale. Tongue pale, anterior region of palate darker. Coloration in life can be seen in Figure 1.
Size. Relative to other species of Bythaelurus, adult B. giddingsi are moderate in size. Our capture technique, using a suction device, was biased toward smaller individuals, and from the submersible we observed but did not capture specimens that seemed to be slightly larger. Two of our specimens (the 40.2 cm female and the 45.3 cm male) appear to be approaching sexual maturity. Our largest specimen (45.3 cm) is about midway in length between the small species of Bythaelurus — B. hispidus (to 29 cm), B. dawsoni (to 35 cm, a subadult male), and B. lutarius (to 39 cm) — and the large species, B. canescens (to 70 cm), and B. immaculatus (to 70 cm) (comparative lengths from Compagno, 1984).
PLATE 2. Photos of dermal denticles from selected regions of the body of the Holotype of Bythaelurus giddingsi sp. nov., CAS 210091, each at 100x magnification. Upper left: dorsal surface of head above eye; upper right: dorsum above gills between lateral line and dorsal midline; middle left: lateral flank above pectoral fin; middle right: abdomen between pectoral and pelvic fins; lower left: dorsal edge of caudal fin; lower right: lateral side of caudal fin.
Etymology. We are pleased to name this species in honor of Al Giddings, underwater filmmaker, naturalist, and friend.
Distribution. All known specimens are from the Galápagos Islands, and were observed and collected from Darwin and Marchena islands between 428–562 m depth, living on the bottom above sand or sand and mud substrates in the vicinity of lava boulders, either over flat bottoms or along slopes to 45o. Specimens were observed but not collected at Cabo Hammond, Fernandina Island, at 496 m, and were photographed at a seamount SE of San Cristobal Island at 461 m (Figure 1). Individuals were observed and photographed using an ROV off North Seymour Island during December, 2005, by Alex Hearn of the Estacion Cientifica Charles Darwin, Galapagos (in litt.). He reported "seeing a number of individuals" living at 500 m depth and photographed one "around 30 cm total length."
Remarks. Bythaelurus giddingsi is easily distinguished from its eight congeners on the basis of its coloration. All others are either pale, dusky, or possess a line of pale spots rather than the irregularly distributed spots of the new species. One interesting aspect of the markings is that the size, arrangement and distribution of the spots are unique to each specimen, and while this spotting pattern is unique to this species, the variable arrangement of spots does not show a consistent species-specific pattern. Moreover, the markings are not bilaterally symmetrical as in most sharks; an individual might have a spot on one side, and may have a smaller, larger, or differently-shaped spot on the other side, or lack it entirely.
There is no apparent difference in dentition between genders of B. giddingsi, however our specimens are limited to females and immature males. Sexually dimporphic heterodonty is present in sexually mature males of other species of scyliorhinids (Springer, 1966; Bass et al., 1975; Nakaya, 1975; Long, 1994).
It is notable that the clumped comb-like dermal denticles of the dorsal edge of caudal fin exhibit the file-like “caudal crest” characteristic seen in several other Bythaelurus and Parmaturus catshark species (Springer, 1979).
Bythaelurus giddingsi is a stouter species than the more elongate, uniformly drab B. immaculatus (Chu & Meng, 1982) and B. incanus Last & Stevens 2008. Its anal-fin base length (about subequal to the interdorsal space) further separates it from B. canescens (Günther, 1878), B. hispidus (Alcock, 1891), and B. lutarius (Springer & D'Aubrey, 1972), which have relatively short anal-fin bases (smaller than their interdorsal distances), and from B. dawsoni (Springer, 1971) which has a relatively longer anal-fin base. The poorly known B. alcocki (Garman, 1913) is said to have a small anal fin and black coloration.
The genus Bythaelurus is widely distributed in the Indian and Pacific oceans, however the distribution of most species of Bythaelurus is best characterized as disjunct (Compagno et al., 2005). Bythaelurus dawsoni is from southern New Zealand, B. clevai is from Madagascar, B. lutarius is from Mozambique and Somalia, B. alcocki is from the Arabian Sea, B. hispidus is from southernmost India, Sri Lanka, and the Andaman Islands, B. immaculatus is from Hainan Island, South China Sea, B. incanus is from northern Australia, B. canescens is from southwestern South America, and B. giddingsi is endemic to the Galápagos Islands. Future studies of the genetics, morphology, and biology of these species will allow a better knowledge of their phylogeny, and future explorations in remote deep waters will undoubtedly discover additional species.
description: Published as part of E, John, Long, Douglas J. & Baldwin, Carole C., 2012, Description of a new species of deepwater catshark, Bythaelurus giddingsi sp. nov., from the Galápagos Islands (Chondrichthyes: Carcharhiniformes: Scyliorhinidae), pp. 48-59 in Zootaxa 3221 on pages 49-58, DOI: 10.5281/zenodo.280250