Spermatological characteristics of Siphoderina aloysiae (Digenea, Cryptogonimidae), an intestinal parasite of Sciaena umbra (Teleostei, Sciaenidae)

Abstract

The ultrastructural organisation of the spermatozoon of Siphoderina aloysiae (Digenea, Cryptogonimidae) is described based upon examination by transmission electron microscopy. Live digeneans were collected from the digestive tract of the Brown meagre Sciaena umbra (Teleostei: Sciaenidae), caught off the Gulf of Gabes in La Chebba (Tunisia). The male gamete of S. aloysiae is a filiform cell, tapered at both extremities, and exhibits typical characteristics of digenean sperm such as two axonemes showing the 9 + ‘1’ trepaxonematan pattern with different lengths. The first axoneme is disorganised and disappears near the anterior nuclear extremity. However, the second axoneme reaches the posterior extremity of the spermatozoon. The latter also contains a nucleus, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, spine-like bodies and granules of glycogen. Cortical microtubules are absent in the anterior extremity of the spermatozoon and appear after the disappearance of the electron-dense material. In addition, the male gamete of S. aloysiae has two mitochondria. The first mitochondrion is associated with the external ornamentation of the plasma membrane and spine-like bodies. The second is more posteriorly located at the nuclear region after the disappearance of the first axoneme. The present study provides new data on the mature male gamete of S. aloysiae that may be useful for the understanding of digenean relationships and phylogenetic studies.