Modified Sperm Ultrastructure in Four Species of Soft-Bodied Echinoids (Echinodermata: Echinothuriidae) From the Bathyal Zone of the Deep Sea

Abstract

Sperm of the bathyal echinothuriid echi noids Phormosomaplacenta, Sperosoma antillense, Ara eosomaftnestratum, and A. beii are similar to those of other echinoids, but have several unique morphological features involving the acrosomal vesicle, the nucleus, and the middlepiece. The acrosomal vesicle shows re gional staining differences including a densely staining central region surrounded by an electron-opaque corn ponent. Sperm nuclei are highly elongated and abruptly taper posteriorly. With the exception of one species, the nuclei lack a distinct centriolar fossa. Intracellular drop lets resembling lipid extend from the extreme posterior region of the middlepiece to form a collar around the proximal portion ofthe axoneme. The presence of lipid like bodies in the middlepiece suggest that the sperm are long-lived and therefore require additional energy stores not found in most metazoan sperm. These findings are compared with a similar study of sperm ultrastructure in three shallow-water echinothuriid species, and their potential significance is discussed in relation to the pres ent knowledge ofechinothuriid reproductive biology.