Jintamas Suwanjarat and Sakol Suwaluk

pp. 413 - 422

Abstract

The ultrastructural characteristics of euspermatogenesis and mature euspermatozoa of Cerithidea
cingulata are described. Euspermatogonia possesses a large round concentric nucleus with one or two nucleoli.
The spermatocyte is characterized by the abundant cytoplasmic organelles and eccentric nucleus with chromatin distributed throughout as small granules. In the early spermatid, euspermiogenesis begins with the
condensation of nucleus, the granular nuclear chromatin changes to fibrillar, lamellar and finally a homogenous and highly electron dense nucleus. The cytoplasm of the early spermatid contains a well developed
Golgi complex with many vesicles and a prominent rough endoplasmic reticulum located between the connection of the two daughter cells. Acrosome formation starts with proacrosomal vesicle which usually appears
close to the well developed Golgi complex. This proacrosomal vesicle differentiates into a pre-attachment
acrosome which then moves anteriorly towards the nucleus and finally attaches to the nuclear apex. The
features of euspermiogenesis and of the mature eusperm observed in Cerithidea cingulata are similar to many
of those in Cerithioideans. The mature acrosome composes of a tapering acrosomal cone, an axial rod and
a basal plate. The middle piece of the mature eusperm comprises four equal and non-helical mitochondrial
elements around the axonemal microtubules. A dense ring structure separates the middle piece from the
glycogen piece. The glycogen piece is the proximal part of the tail which consists of an axoneme surrounded by nine tracts of dense glycogen granules, while the end piece of the tail lacks glycogen. Euspermatozoa and
euspermatogenesis of Cerithidea cingulata, though showing some differences between species, do share a
number of basic structure features which distinguish potamidid snails from other relatively close families.