The size of each species having a calcareous shell was recorded in at least 10 Holocene faunas of the following groups: marine, freshwater, and land gastropods; marine and freshwater pelecypods; and benthonic Foraminiferida. No pelecypod species living in the Arctic, the Antarctic, or the deep sea (2,000 m or deeper) attains a size of 100 mm. No marine gastropod species living in the Arctic or Antarctic attains a size of 150 mm. The largest living species of marine gastropods and pelecypods live in the western part of the Pacific and eastern part of the Indian Ocean. The largest living calcareous Foraminiferida also lives in the same general region. More large-size freshwater pelecypods live in warm water, and this trend applies to a lesser extent to freshwater gastropods The largest freshwater gastropods and pelecypods, as well as the largest land gastropods, all live in the lower latitudes. Large calcareous Foraminiferida live in warm water, but large agglutinated Foraminiferida live in cold water.

Some geographic anomalies occur, and one of these is the uncommonly high percentage of small-size (10 mm or less) species of marine gastropods and pelecypods in the Antarctic.

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