Comprehensive Description

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General Description

The shell is large, up to 110 mm long, rather thickwalled and solid. It is moderately short, wedge-shaped-modioliform, little variable, and modestly inflated. The shell is equivalve, with a length/height ratio of 1.8-1.9. The beaks are almost terminal to terminal or even slightly protruding anteriorly. The anterior margin is narrowly rounded, whilst the ventral margin is visibly concave in the middle part, occasionally with a well-marked crease at the end of the first fourth or fifth of the valve, which makes the anterior part appear bent ventrally. The posterior margin is ventrally broadly rounded ventrally, and the postero-dorsal margin is markedly convex. The postero-dorsal corner is well rounded. The ligament plate is more or less arched. The exterior has well developed, dense, irregular growth lines. The umbone is broad and somewhat flattened.

The periostracum is thick, dark chestnut brown in colour, and is smooth and dull, with no periostracal hairs and no byssal endplates. The umbonal region is generally eroded in half-grown and larger specimens. The hinge is toothless, with the anterior hinge margin strengthened to a buttress along the valve edge and protruding ventrally. Posteriorly, the buttress does not abruptly end, but gradually passes into the subligamental shell ridge. The ligament is opisthodetic, strong, and extends to more or less in front of the postero-dorsal corner (depending on the situationof the latter), and ends abruptly without any taper. The subligamental shell ridge is faint, visible along two thirds of ligament length and from both ventral and lateral perspectives. The anterior adductor scar is small and oval, under or just behind the umbone. The posterior adductor scar is a large rounded-oval, united with the long scar of the posterior pedal and byssus retractor muscle. The scar of the anterior bundle of the posterior retractor is not at all or hardly separated from that of the posterior bundle, with the anterior end situated under the posterior third or fourth of the ligament. The anterior byssus retractor scar is in the posterior part of the umbonal cavity, well behind the beaks, and is visible only when viewed from posterior and ventrally. The pallial line is only weakly concave in the middle.

The shell without periostracum is a dull whitish colour, whilst the interior is white and slightly nacreous.

The animal is not known, but judging from the muscle scars, it is evident that it has an almost continuous multibundle posterior retractor.

(Cosel, 2002)


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