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monoplacophora
Monoplacophora, meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell now living at the bottom of the deep sea. Extant representatives were unknown until 1952; previously they were known only from the fossil record.
Although the shell of many monoplacophorans is limpet-like in shape, they are not gastropods and are not closely related to gastropods.
== Definition ==
Discussion about monoplacophorans is made difficult by the slippery definition of the taxon; some authors take it to refer to all non-gastropod molluscs with a single shell, or all single-shelled molluscs with serially repeated units; whereas other workers restrict the definition to cap-shaped forms, excluding spiral and other shapes of shell. The inclusion of the gastropod-like Bellerophontoidea within the group is also contentious.
One attempt to resolve this confusion was to separate out the predominantly coiled helcionelloids from the traditional, cap-like tergomyans, this latter group containing extant Tryblidiids.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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