Spermatozoa of Ciona intestinalis and analysis of ascidian fertilization

Abstract

The complex array of vestments which surrounds the ascidian oocyte indicates that spermatozoa of these urochordates may be highly modified to effect penetration through the egg‐envelopes and to achieve successful fusion with the female gamete. Examination of the spermatozoa of Ciona intestinalis reveals, however, that they lack an acrosomal vesicle and do not possess detectable amounts of actin. Furthermore, the spermatozoa do not undergo observable morphological alterations when exposed to ammoniated seawater, a treatment known to produce aggregation and an acrosome reaction in other organisms. Ciona spermatozoa do contain significant quantities of proteases. It is hypothesized that the localization of these enzymes may be related to the ridge‐like surface ornamentation which is observed as a component of the head region of Ciona spermatozoa.