Sperm characters of the digenean Prosorhynchus aculeatus Odhner, 1905 (Bucephalidae), a parasite of the marine fish Conger conger (Linnaeus, 1758) (Congridae)

Abstract

Within the Digenea, the family Bucephalidae includes numerous species parasitizing mainly marine and freshwater fishes. This family includes five recognized subfamilies, and ultrastructural data on their sperm cells are very scarce. The existing data are restricted to the subfamily Bucephalinae. Thus, the present study is the first complete analysis of the sperm cell of a bucephalid belonging to the subfamily Prosorhynchinae. Herein, we describe the ultrastructure of the mature spermatozoon of Prosorhynchus aculeatus, a parasite of the conger eel Conger conger, assessed by means of transmission electron microscopy (TEM). The spermatozoon of P. aculeatus is a filiform cell that presents two axonemes of the 9+‘1’ pattern of trepaxonematan Platyhelminthes, parallel cortical microtubules, mitochondrion, nucleus, external ornamentation of the plasma membrane, spine-like bodies and a large amount of glycogen granules. According to the anterior location of the external ornamentation of the plasma membrane, P. aculeatus presents a Quilichini et al.’s type 1 spermatozoon. With respect to the posterior extremity, the sperm cell of P. aculeatus corresponds to the Quilichini et al.’s cryptogonimidean type. Our results are compared with those of the two previously studied bucephalids (Bucephalinae), Prosorhynchoides gracilescens and Pseudorhipidocotyle elopichthys.