Comprehensive Description

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General Description

The shell is stout, elongate in outline, with a height/ length ratio of 0.53 and is equivalve. The periosracum is eroded in the umbonal region, and is dehiscent, thin, glossy dirty-pinkish in colour and wrinkled with short concentric lamellae that are perpendicular to the surface, developed mostly at the periphery. The shell has a sculpture of growth lines and low irregular concentric ridges. The escutcheon is shallow, and the lunule is indistinct. The shell is inequilateral with the umbo situated at 33% from 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 margin is broadly rounded. The posterior margin is acutely rounded and the posterior-dorsal margin is nearly straight. The pallial line is indistinct and slightly impressed. The anterior adductor scar is irregularly oval and slightly impressed to the rear. The anterior pedal retractor scar is shallow. 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 nearly abrupt posterior end, occupying 29% of the valve length. Along the distal part of the base of the nymph there is a very slight depression. A fibrous layer of ligament, which attaches to the nymph, is 70% of the posterior lamellar layer.

Dentition of the right valve: ventral cardinal (1) is stout, shelf-shaped and radiates obliquely anteriorwards. The 3a-ramus is thin, lamellate and parallel to the anterior-dorsal shell margin, fused in its low proximal part with the anterior edge of the 3b-ramus. The 3b-ramus is broad and low, with slightly raising anterior and posterior edges and a concave top surface. The anterior edge usually radiates ventrally, whilst the posterior edge radiates posteriorly. The posterior nymphal ridge is elongate, very low and occupies less than a half of the nymph.

Dentition of left valve: the 2a-ramus is thin, shelf-like and subparallel to the anterior-dorsal shell margin. It is fused in its proximal part with the proximal part of the 2b-ramus. The 2b-ramus is thicker and shorter than 2a, and radiated ventrally. The 4b-tooth is elongate, occupying less than half of the nymph, and radiates posteriorwards.

(Krylova & Sahling, 2006)


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