On the Morphology of Actiniarian Larvae

Abstract

Planktonic larvae of the Athenaria correspond in a number of morphological characteristics to plankto-trophic thenarian planulae. In edwardsiid planulae there are often, during the later part of the planktonic phase, a well-developed aboral physa-“Anlage” and six triangular tentacles. Holotrichous haplonemes are not uncommon in actiniarian planulae. This nemato-cyst type is, however, limited to the larva stage in the edwardsiid and some thenarian species. The phylogenetical connection between the edwardsiid and the planktotrophic thenarian planulae is stressed The striking morphological resemblances between madreporarian and lecithotrophic planulae of the family Actiniidae indicate a close phylogenetic connection between the two planula types.