SPERM MORPHOLOGY AND ANATOMY OF THE GENITAL ORGANS IN MESODASYS LATICAUDATUS REMANE, 1951 (GASTROTRICHA, MACRODASYIDA)

At complete sexual maturity, Mesodasys laticaudatus is a simultaneous hermaphrodite. A single, unpaired ovary is present, dorsal to the inte stine, at about half of the body length. Eight to ten oocytes are visi ble, increasing in size in caudo-cephalic direction. No oviduct is vis ible, which suggests egg release through body rupture. The testes are paired and symmetrically disposed in the same area of the ovary. They contain germ cells in various stages of maturation and are connected t hrough ducts to a caudal organ probably acting as a copulatory structu re. The spermatozoa have an acrosome ending apically with a spiral sta ircase portion, a spring-shaped nucleus surrounding a variable number of mitochondria, and a tail. This last has a typical 9+2 axoneme, surr ounded by a complex striated cylinder. Our observations are not incons istent with the hypothesis of a dermal impregnation in Mesodasys.