title: Ultrastructure of spermatogenesis and mature spermatozoa in the flatworm Prosthiostomum siphunculus (Polycladida, Cotylea).
abstract: This is the first study investigating spermatogenesis and spermatozoan ultrastructure in the polyclad flatworm Prosthiostomum siphunculus. The testes are numerous and scattered as follicles ventrally between the digestive ramifications. Each follicle contains the different stages of sperm differentiation. Spermatocytes and spermatids derive from a spermatogonium and the spermatids remain connected by intercellular bridges. Chromatoid bodies are present in the cytoplasm of spermatogonia up to spermatids. During early spermiogenesis, a differentiation zone appears in the distal part of spermatids. A ring of microtubules extends along the entire sperm shaft just beneath the cell membrane. An intercentriolar body is present and gives rise to two axonemes, each with a 9 + "1" micro-tubular pattern. Development of the spermatid leads to cell elongation and formation of a filiform, mature spermatozoon with two free flagella and with cortical microtubules along the sperm shaft. The flagella exit the sperm shaft at different levels, a finding common for acotyleans, but so far unique for cotylean polyclads. The Golgi complex produces numerous electron-dense bodies of two types and of different sizes. These bodies are located around a perinuclear row of mitochondria. The elongated nucleus extends almost along the entire sperm body. The nucleus is wide in the proximal part and becomes narrow going towards the distal end. Thread-like chromatin mixed with electron-dense intranuclear spindle-shaped bodies are present throughout nucleus. The general sperm ultrastructure, the presence of intranuclear bodies and a second type of cytoplasmic electron-dense bodies may provide characters useful for phylogenetic analysis.
authors.affiliation: Université de Tunis El-Manar, Faculté des Sciences de Tunis, UR11ES12 Biologie de la Reproduction et du Développement Animal, Tunis, 2092, Tunisie.
authors.forename: Mehrez
authors.initials: M
authors.lastname: Gammoudi
authors.affiliation: Research Unit Evolutionary Developmental Biology, Institute of Zoology, University of Innsbruck, Technikerstr. 25, Innsbruck, 6020, Austria.
authors.forename: Willi
authors.initials: W
authors.lastname: Salvenmoser
authors.affiliation: Department of Zoology, College of Science, King Saud University, P.O. Box 2455, Riyadh, Saudi Arabia.
authors.forename: Abdel Halim
authors.initials: AH
authors.lastname: Harrath
authors.affiliation: Université de Tunis El-Manar, Faculté des Sciences de Tunis, UR11ES12 Biologie de la Reproduction et du Développement Animal, Tunis, 2092, Tunisie.
authors.forename: Saïda
authors.initials: S
authors.lastname: Tekaya
authors.affiliation: Research Unit Evolutionary Developmental Biology, Institute of Zoology, University of Innsbruck, Technikerstr. 25, Innsbruck, 6020, Austria.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Egger
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure; D008297:Male; D046529:Microscopy, Electron, Transmission; D008870:Microtubules / Q000648:ultrastructure; D010986:Platyhelminths / Q000378:metabolism*; D013091:Spermatogenesis / Q000502:physiology*; D013093:Spermatogonia / Q000648:ultrastructure*; D013094:Spermatozoa / Q000648:ultrastructure
keywords: apomorphies; chromatoid bodies; polyclads; spermatogenesis; spermiogenesis