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MACTRIDAE |
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Mactra pusilla A. Adams, 1856 Description: Shape elongate-ovate; length greater than height, umbo slightly posterior to midline; anterior and posterior ends with ridges from umbo to antero-ventral and postero-ventral margin. Exterior smooth except for commarginal growth lines; dorsal regions above anterior and posterior ridges with strong radiating riblets. Interior purple or white, with muscle scars and pallial line well defined, pallial sinus deep. Interior callus thickening with age, initially thin and mainly purple, becoming thick and mainly white with maturity. Hinge as for family. Ligament internal. Shell fawn, often with brown rays, and usually with an elongate white area along the margin immediately below, and either side of, umbo. Size: Up to 39 mm in length. Distribution: Endemic to Australia: Cooktown, Qld, southwards to Tas. Habitat: Lives in sand and sandy mud in the shallow subtidal zone and down to 50 m. Often washed up on beaches. Moderately common. Remarks: Traditionally, this species has been characterised by the radiating brown lines, but they are absent on many NSW specimens. A better feature for identification is the strong radial sculpture on the regions above the anterior and posterior ridges, allied with relatively smooth sculpture of the rest of the shell. On the basis of this radial sculpture, Mactra pusilla could be mistaken for a juvenile M. eximia, but that is more ovate and the pallial sinus is much shorter. Fig. 1: Dolls Point, Georges River, Sydney (C.368329) |
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