title: [An ultrastructural study of oogenesis in the planarian Schmidtea mediterranea (Platyhelminthe, Paludicola)].
abstract: The ovary of the freshwater planarian Schmidtea mediterranea has been studied for the first time using both light and electron microscopy methods. The ultrastructure of the ovary revealed two types of cells: accessory cells and germinal cells at various stages of differentiation, distributed along a maturation axis. Initially, oogonia underwent cytoplasm growth due to the development of organelles, such as endoplasmic reticulum, Golgi complex, and mitochondria, which are all involved in the production of cytoplasmic inclusions or yolk globules. It is shown that the chromatoid body and fibrogranular aggregates may participate in the synthesis of vitelline inclusions. When completely mature, the oocytes have become larger, due to the accumulation of nutritive inclusions, which are round in shape and have a paracrystalline structure. These inclusions are interpreted as being yolk globules and may represent a kind of nutritive material for the developing embryo. These ultrastructural features of the ovary agree with the available phylogenetic tree, based on morphological and karyological characters that considers Schmidtea group as a genus and not a subgenus. The presence of sperm between the oocytes suggests that fertilization may occur within the ovary, representing an uncommon condition within the Triclads, in which fertilization usually takes places outside of the ovaries.
authors.affiliation: Fetal Programming of Diseases, Research Chair, Zoology Department, College of Science, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Abdul Halim
authors.initials: AH
authors.lastname: Harrath
authors.forename: Saleh H
authors.initials: SH
authors.lastname: Alwasal
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Alhazza
authors.forename: Fathia
authors.initials: F
authors.lastname: Zghal
authors.forename: Saida
authors.initials: S
authors.lastname: Tekaya
mesh_terms: D000818:Animals; D008854:Microscopy, Electron; D009866:Oogenesis; D009867:Oogonia / Q000648:ultrastructure*; D010932:Planarians / Q000502:physiology*