Comparative Morphology of Echinoderm Sperm and Possible Phylogenetic Implications

Abstract

The sperm morphology of at least 7 crinoids, 11 ophiuroids, 23 asteroids, 23 holothuroids, and 37 echinoids is known. For all the known crinoids, ophiuroids, and asteroids, the sperm are spherical, while those of echinoids are conical. Holothuroid sperm are basically spherical, with two exceptions: cylindrical in Cucumaria lubrica and tabloid in Cucumaria pseudocurata. The possible implications of sperm morphology in the mode of fertilization and in echinoderm phylogeny are discussed.