Neotrigonia is a very active, free-living bivalve, yet its adult foot contains a rather extensive, though nonfunctional, byssal apparatus. Is this apparatus a phylogenetic residue, reduced from its form in a byssate adult ancestor, or does it function at an earlier stage of trigonian ontogeny? There is no firm evidence for the existence of a byssus in Mesozoic adult trigonians. Gould favors the hypothesis that the trigonian byssus is functional in juveniles for two reasons: Most, and perhaps all, bivalves are byssally attached in the post-larva and several prolong this habit into later juvenile stages. In the single juvenile specimen examined, the byssal organs were better developed than in adults.

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