title: Investigation of the ultrastructure of Dendrocoelum constrictum (Platyhelminthes, Tricladida) spermatogenesis and mature spermatozoa.
abstract: To add to our understanding of dendrocoelid spermatozoa and to describe additional phylogenetic characters, the ultrastructure of the testis was investigated in the subterranean freshwater planarian Dendrocoelum constrictum. This is the first study investigating spermatogenesis and spermatozoon ultrastructure in a subterranean freshwater planarian species. We found that the basic structure of spermatozoa in D. constrictum is similar to that of other Tricladida that have been studied previously. In fact, D. constrictum spermatozoa possess an elongated nucleus, one giant mitochondrion, and two subterminal flagella with a 9+'1' pattern. The flagella emerge together from one side of the spermatozoon. However, D. constrictum has some characteristics that have not yet been described for other freshwater planarians. In fact, the number of cortical microtubules reaches the maximum number in the anterior and middle part of region I, and then decrease until they disappear towards the posterior extremity of the spermatozoon. The extreme tip of the anterior region of the spermatozoon exhibits a specific external ornamentation of the plasma membrane.
authors.affiliation: Zoology Department, College of Science, King Saud University, PO Box 2455, 11451 Riyadh, Saudi Arabia. Electronic address: halim.harrath@laposte.net.
authors.forename: Abdel Halim
authors.initials: AH
authors.lastname: Harrath
authors.affiliation: University of Tunis El Manar, Faculty of Science of Tunis, UR11ES12 Animal Reproduction and Developmental Biology, 2092 Tunis, Tunisia.
authors.forename: Mehrez
authors.initials: M
authors.lastname: Gammoudi
authors.affiliation: Zoology Department, College of Science, King Saud University, PO Box 2455, 11451 Riyadh, Saudi Arabia.
authors.forename: Lamjed
authors.initials: L
authors.lastname: Mansour
authors.affiliation: Zoology Department, College of Science, King Saud University, PO Box 2455, 11451 Riyadh, Saudi Arabia.
authors.forename: Mukhtar
authors.initials: M
authors.lastname: Ahmed
authors.affiliation: Zoology Department, College of Science, King Saud University, PO Box 2455, 11451 Riyadh, Saudi Arabia; Animal Production Research Center Nitra, Luzianky, Slovakia; Constantine the Philosopher University, Nitra, Slovakia.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Sirotkin
authors.affiliation: Zoology Department, College of Science, King Saud University, PO Box 2455, 11451 Riyadh, Saudi Arabia.
authors.forename: Suliman Y
authors.initials: SY
authors.lastname: Al Omar
authors.affiliation: Zoology Department, College of Science, King Saud University, PO Box 2455, 11451 Riyadh, Saudi Arabia.
authors.forename: Khalid E
authors.initials: KE
authors.lastname: Ibrahim
authors.affiliation: Zoology Department, College of Science, King Saud University, PO Box 2455, 11451 Riyadh, Saudi Arabia.
authors.forename: Saleh H
authors.initials: SH
authors.lastname: Alwasel
mesh_terms: D000818:Animals; D005260:Female; D005407:Flagella / Q000502:physiology / Q000648:ultrastructure; D008297:Male; D046529:Microscopy, Electron, Transmission; D008870:Microtubules / Q000502:physiology / Q000648:ultrastructure; D009865:Oocytes / Q000502:physiology / Q000648:ultrastructure; D010986:Platyhelminths / Q000502:physiology*; D013091:Spermatogenesis / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology* / Q000648:ultrastructure*
keywords: Dendrocoelum constrictum; Free-living flatworm; Mature spermatozoon; Spermatogenesis; Ultrastructure