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Family Mactridae - trough shells
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Order |
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Class |
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Bivalvia |
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No. of Genera in Ref. |
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No. of Species in Ref. |
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Environment |
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Fresh : Yes |
Brackish : Yes |
Marine : Yes |
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First Fossil Record |
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Remark |
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Shell equivalve, ovate or trigonal to transversely elongated, closed to somewhat gaping posteriorly. Umbones prosogyrate, more or less prominent. Outer surface smooth or mostly concentrically sculptured, often with an abvious periostracum. External ligament short and not prominent, just behind the umbones; internal ligament well developed, set in each valve in a deep trigonal pit of the hinge plate and pointing towards the umbo. Hinge characteristic, each valve with two cardinal teeth and smooth or striated, more or less developed, lateal teeth; cardinal teeth of the left valve forming an inverted V-shaped process; delicate additional cardinal lamellae often present in either valve. Interior of shell porcelaneous. Two, often subequal, adductor muscle scars. Pallial line with a well-developed sinus. Internal margins usually smooth. Gills of eulamellibranchiate type, with generally smooth branchial sheets; outer demibranch expanded above the ctenidial axis. Foot large and compressed, heeled, without a byssus. Siphons united, generally rather short, naked or sheathed with an expansion of the periostracum, papillate on top. Mantle margins smooth, more or less cuticularly united or fused ventrally, with a large pedal opening anteriorly and an additional aperture beneath the inhalant siphon. Active burrowers of sandy to muddy bottoms. Suspension filter-feeding animals. Sexes separate. Development with a free-swimming larval stage. Mactridae represent generally species of secondary importance in the harvest of edible bivalves in the area, although a few species are quite regularly fished locally (Ref. 348). |
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