Ctenacis Compagno, 1973

3.3.1 | Genus Ctenacis Compagno, 1973 View in CoL

Synonymy: Ctenacis Compagno, 1973: 258 , fig. 1 ( type species Triakis fehlmanii Springer, 1968 by monotypy); Compagno, 1984: 370; Compagno, 1988: 183; Compagno, 1999: 481.

Species: Two species – Ctenacis fehlmanni (Figure 3) and Ctenacis magnificum (Figures 4 and 5).

Diagnosis: Proscylliid sharks with males of C. magnificum adult at 472 mm L T and females of C. fehlmanni adult at 460 mm L T. Head broad and rather long, length 21% – 23% of total length. Fifth gill opening over half length of third. Nostril width about 1.1 – 1.2 in internarial width. Anterior nasal flaps small to moderately large, with edges anterior to upper symphysis (Figure 6a,b); margins of anterior and posterior nasal flaps fringed (barely evident on anterior nasal flaps of C. magnificum ); posterior nasal flaps moderately large. Sexual heterodonty present in at least one species; adult males of C. magnificum with mostly three cusps, with median cusp taller (Figure 7a); females with mostly five cusps; tooth file counts 80 – 86 in upper jaw. Length of head and trunk from snout tip to vent about 44% – 46% of total length. Body relatively stout, caudal peduncle slightly compressed, width greater than its height. Lateral trunk denticles of adults moderately broad to very broad, with thick, short to moderately long medial cusps; poorly to well-developed lateral cusps; two median ridges on crowns, further apart centrally, converging anteriorly and to tip of cusp posteriorly; ectodermal pits present, restricted to anterior portion of crown (Figure 8a,b). Distance between pectoral and pelvic bases shorter than head length. Claspers of adult male (based on C. magnificum ) moderately long and slender, extending well posterior to free rear tips of pelvic fins; dorsal edges of clasper groove fused together between apopyle and hypopyle; cover rhipidion small, narrow but elongate; rhipidion long, fleshy, exposed for most of its length and not concealed by cover rhipidion; exorhipidion without clasper hooks on its distal edge (Figure 9). First dorsal origin over pectoral inner margins or just posterior to free rear tip. Length of first dorsal fin from origin to free rear tip 1.3 – 1.8 in interdorsal space. Postanal space slightly longer or slightly shorter than anal base. Anal origin slightly posterior to second dorsal origin, anal insertion about under second dorsal insertion. Caudal fin short, not tapelike, length of dorsal caudal margin 21% – 23% of total length.

Internal carotid foramina of cranium located close together, the distance between them about four times distance between each internal carotid foramen and their adjacent stapedial foramen; anterior fontanelle broad, wider than it is long; edge of sphenopterotic ridge diagonal to longitudinal axis of cranium in dorsal view (Figure 1a – d). Total vertebral counts 136 – 143, precaudal diplospondylous (DP) counts 48 – 56, monospondylous (MP) counts 26.6% – 28.6%, DP counts 35.2% – 39.2%, and caudal diplospondylous (DC) counts 34.3% – 36.0% of total count. DP/MP ratios 1.2 – 1.5. Spiral intestinal valve with 10 turns. Color pattern of large dark blotches, saddles and spots on a light ground color.

Distribution: Indian Ocean only. Ctenacis fehlmanni is known from the northwestern Indian Ocean and C. magnificum from the northeastern Indian Ocean (Figure 10).