All epifaunal and most infaunal pelecypods are suspension feeders, but all protobranchs, including the solemyids, and almost all tellinids and semelids are deposit feeders. The protobranchs are the more diverse in cold and temperature water, and the tellinids and semelids are the more diverse in warm water. The 20°C isotherm divides those pelecypod faunas dominated by protobranchs from those dominated by tellinids and semelids. The abyssal fauna has a larger percentage of deposit feeders than any shallow-water fauna because of the greater diversity of protobranchs. The Antarctic fauna is the only one devoid of tellinaceans.

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