Ultrastructural study of mature sperm ofPomphorhynchus laevisMüller (Acanthocephala: Palaeacanthocephala), a fish parasite

Abstract

Summary Ultrastructural observations on mature sperm of Pomphorhynchus laevis (Muller, 1776), the dominant acanthocephalan parasite of fish from the River Brenta, were carried out by scanning (SEM) and transmission electron microscopy Adult males of P. laevis were obtained from the digestive tract of Leucisctcs cephalus (Pisces: Cyprinidae). The spermatozoon of P. laevis is inverted with respect to conventional sperm models; it is filiform and consists of an anterior flagellar apparatus and a posterior nucleocytoplasmic derivative. The latter includes a layer of condensed chromatin beneath the plasma membrane opposite to the flagellum, numerous large subspherical electron dense inclusions, glycogen deposits and a pentalaminar structure next to the flagellum. The nucleocytoplasmic derivative terminates caudally with a flat lamina devoid of the dense inclusions and glycogen deposits. Proceeding through the posterior lamina, the 9+2 axoneme progressively disorganizes. The ultrastructural organization resembl...