Galápagos Catshark

description

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); 1 st gill openings 70 (17.4, 21.7); 2 nd gill openings 82 (20.3, 25.4); 3 rd gill openings 89 (22.1, 27.6); 4 th gill openings 92 (22.9, 28.5); 5 th gill openings (= head length) 96.5 (24.0, 29.9); pectoral origins 90 (22.4, 27.9); pelvic origins 190 (47.3, 58.9); 1 st dorsal origin 187 (46.5, 57.9); 2 nd 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); 1 st and 2 nd dorsal origins 72 (17.9, 22.3); 1 st and 2 nd dorsal bases 43 (10.7, 13.3); 2 nd dorsal and upper caudal origins 53.5 (13.3, 16.7); 2 nd 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 an

Description of a new species of deepwater catshark, Bythaelurus giddingsi sp. nov., from the Galápagos Islands (Chondrichthyes: Carcharhiniformes: Scyliorhinidae)

diagnosis

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 of a new species of deepwater catshark, Bythaelurus giddingsi sp. nov., from the Galápagos Islands (Chondrichthyes: Carcharhiniformes: Scyliorhinidae)

discussion

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 se

Description of a new species of deepwater catshark, Bythaelurus giddingsi sp. nov., from the Galápagos Islands (Chondrichthyes: Carcharhiniformes: Scyliorhinidae)

distribution

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 45 o. 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. "

Description of a new species of deepwater catshark, Bythaelurus giddingsi sp. nov., from the Galápagos Islands (Chondrichthyes: Carcharhiniformes: Scyliorhinidae)