The functional anatomy of the echinoderm spermatozoon and its interaction with the egg at fertilization

Abstract

The ultrastructure of spermatozoa representing four echinoderm classes is presented. Sperm of these four classes are strikingly similar in their morphology, particularly with regard to the acrosomal region. This region consists of two major components, an acrosomal vesicle with a complete bounding membrane and the surrounding periacrosomal material. The events of the acrosomal reaction in an echinoid and a holothurian are described in detail and the functional role of the acrosomal region during fertilization is presented. The role of extracellular coats in the establishment of gamete specificity is also discussed with reference to echinoids. The later events of fertilization in echinoids, including sperm incorporation, pronuclear development, and pronuclear fusion are reviewed. © 1975 by the American Society of Zoologists.