Spermatological characters of the caryophyllidean cestode Khawia sinensis Hsü, 1935, a carp parasite.

Spermatological characters of the caryophyllidean tapeworm Khawia sinensis (Lytocestidae), a carp parasite, have been investigated for the first time. The process of the spermatozoon formation corresponds in basic pattern to that of Khawia armeniaca (Brunanská and Poddubnaya, Parasitol Res 99: 449-454, 2006). The presence of dense material at the early stages of spermiogenesis, the intercentriolar body, flagellar rotation (free flagellum plus flagellar bud), and a complete proximodistal fusion have been reported. In addition, it was shown that the developing spermatids may exhibit a free flagellum distally. The unipartite young spermatid and/or mature spermatozoon of K. sinensis consist of one axoneme of the 9 + "1" trepaxonematan pattern, nucleus, and cortical microtubules. These components are situated in cytoplasm, which is either electrolucent (young spermatid) or moderately electrodense (mature spermatozoon). The crested body is absent. The proximal extremity of the male gamete of K. sinensis contains a centriole and a few (up to six) cortical microtubules arranged in a semicircle. The number of cortical microtubules increases distally and reaches maximum (up to 15) in the middle part of the filiform cell, which contains the nucleus. The posterior extremity of the mature spermatozoon exhibits elements of the disorganized axoneme. The ultrastructural characteristics of spermiogenesis and the mature spermatozoon of K. sinensis support basal position of the Caryophyllidea (and Spathebothriidea) relative to other eucestode orders.