title: Spermiogenesis and spermatozoon of the tapeworm Ligula intestinalis (Diphyllobothriidea): phylogenetic implications.
abstract: Using transmission electron microscopy, spermiogenesis and the spermatozoon ultrastructural organization are described in Ligula intestinalis (Linnaeus, 1758) (Diphyllobothriidea), a parasite of the great crested grebe Podiceps cristatus (Linnaeus, 1758). Spermiogenesis starts with the differentiation zone of 2 striated rootlets, 2 centrioles giving rise to 2 flagella, and an intercentriolar body. The latter is composed of 5 electron-dense layers separating 4 electron-lucent layers. In the early stages of spermiogenesis, an electron-dense material is present in the apical region of the differentiation zone. Later, the flagella undergo a rotation and fuse with the cytoplasmic extension in a proximo-distal process. The spermatozoon contains 2 axonemes with a 9 + "1" trepaxonematan pattern, the nucleus, the cortical microtubules, and an electron-dense zone. The spermatozoon anterior extremity in L. intestinalis is characterized by the absence of crested bodies and a ring of electron-dense cortical microtubules. Some characters of spermiogenesis and spermatozoon in L. intestinalis confirm the recent splitting of "Pseudophyllidea" into 2 new orders, i.e., Bothriocephalidea and Diphyllobothriidea. The process of spermiogenesis is similar in both orders for the "type I" of spermiogenesis and the presence of electron-dense material. However, the intercentriolar body is clearly more developed in the Diphyllobothriidea than in the Bothriocephalidea. Moreover, these 2 orders seem to differ in the presence or absence of a ring of electron-dense cortical microtubules in the anterior extremity of the spermatozoon.
authors.affiliation: Institute of Parasitology, Biology Centre of the Czech Academy of Sciences, Czech Republic. levron@paru.cas.cz
authors.forename: Céline
authors.initials: C
authors.lastname: Levron
authors.forename: Jiljí
authors.initials: J
authors.lastname: Sitko
authors.forename: Tomás
authors.initials: T
authors.lastname: Scholz
mesh_terms: D000818:Animals; D001715:Bird Diseases / Q000469:parasitology; D001717:Birds; D002589:Cestoda / Q000145:classification* / Q000502:physiology* / Q000648:ultrastructure; D002590:Cestode Infections / Q000469:parasitology / Q000662:veterinary; D018153:Czech Republic; D008297:Male; D046529:Microscopy, Electron, Transmission; D010802:Phylogeny; D013091:Spermatogenesis / Q000502:physiology*; D013094:Spermatozoa / Q000648:ultrastructure*