Calyptogena makranensis Krylova & Sahling , 2006
The shell is stout and elongate in outline. The value height/ length ratio is 0.50, and the shell is equivalve. The valves are more flattened towards the dorsal margin. The periostracum was eroded in the umbonal regions, and is thin, glossy, yellow-brownish in colour and darker and wrinkled towards the periphery. The sculpture of the shell consists of growth lines and low irregular concentric ridges. The escutcheon is moderate and is limited by a sharp ridge. The lunule is narrow and long, limited by slightly raised ridges. The shell is inequilateral, with the umbo situated at 34% of the length form the anterior end of the valve. The umbones are prosogyrate and low. The beaks are slightly enrolled and nearly touching each other. The anterior-dorsal margin is straight, whilst the anterior and posteriors margin are rounded. The ventral margin is nearly straight, and the posterior-dorsal margin is straight with a posterior obtuse angle. The pallial line is distinct and slightly impressed. The anterior adductor scar is irregularly oval and slightly impressed to the rear. The anterior pedal retractor scar is shallowly impressed, and is not fused with the anterior adductor scar, but is connected to it by a narrow line. The posterior adductor scar is clearly visible but not impressed. It is as wide as it is high, pear-shaped, and fused to the posterior pedal retractor scar. The nymph is strong, with a sloping posterior end and occupies 32% of the valve length. There is a fibrous layer of ligament with attaches to the nymph, and is 77% of the posterior lamellar layer.
Dentition of the right valve: the ventral cardinal (1) is thin and shelf-shaped, radiating obliquely anteriorwards. The 3a-ramus is thin, lamellate and is parallel to the anterior-dorsal shell margin. It is fused in its low proximal part with the naterior edge of the 3b-ramus. The 3b-ramus is broad and low, with slightly elevated anterior and posterior edges and a concave top surface. The anterior edge usually radiates ventrally, whilst the posterior edge is parallel to the posterior nymphal ridge. The posterior nymphal ridge is elongate, occupying nearly half the length of the nymph.
Dentition of the left valve: the 2a-ramus is shelf-like and is sub-parallel to the anterior-dorsal shell margin, fused in its proximal part with the proximal part of the 2b-ramus. The 2b-ramus is thicker and shorter than 2a, radiating ventralwards. The 4b-tooth is elongate, occupying nearly half of the nymph, subparallel to the posterior-dorsal shell margin.
(Krylova & Sahling, 2006)
Ecology and Distribution
Makran continental margin off Pakistan, northwestern Indian Ocean (24°32.94'N, 64°15.70'E), 2,213-2,336 m depth (Krylova & Sahling, 2006)