Potential for paired vestibules in plutei (Echinodermata, Echinoidea)

Abstract

Abstract. Echinoids are generally thought to develop only a single ectodermal invagination (V1), which expands into a vestibule and contributes to the formation of the juvenile rudiment on the left side of the larval body. However, in 2 echinoid species, Strongylocentrotus purpuratus and Dendraster excentricus, a second invagination (V2) was observed to form on the right side of the larval body exactly opposite V1. Formation of the invaginations was followed and characterized using light microscopy and antibodies directed against the S2amide echinoderm neuropeptide as a morphological tag. V2 consistently formed later than V1, and appeared capable of contributing to the formation of a second rudiment when it received the appropriate mesodermal influence from contact with a hydrocoel. Otherwise, in both species, V2 formed a skeletal element that has not been previously described in this location. Because of the location, shape, and timing of its formation, V2, like V1, appears to have the innate ability of the larval ectoderm to contribute to juvenile rudiment formation.