The functional morphology of the larva, and the post-larval development of <i>Venus striatula</i> (Da Costa)

Abstract

SUMMARY The functional morphology of the veliger, pediveliger, and early post-larva of Venus striatula is described. Settlement takes place at a length of 220- 240 /u, and is marked by the rapid loss of the velum, functioning of the byssus gland, and commencement of secretion of the post-larval shell (dissoconch). With the exception of the loss of the velum, the changes which occur at metamorphosis take place relatively slowly. The significance to phylogeny of the mode of development of certain organs in the post-larva is discussed. It is concluded that the form of many of the organs in development, especially of those organs concerned in producing a respiratory and feeding current, are juvenile adaptations, resulting in the early functional re-adjustment of the free-swimming larval habit to a bottom-living habit, but having little or no phylogenetic significance.