01642nas a2200193   4500008004100000020001400041245007200055210006900127260000800196300001200204490000800216520110400224100001401328700001301342700001501355700001801370700001501388856004501403       2011                        eng d  a0720-213X00aSpermatogenesis and the structure of the testes in Nemertodermatida0 aSpermatogenesis and the structure of the testes in Nemertodermat  cDec  a273-2820 v1303 aThe ultrastructure of the testes in two representatives of the enigmatic taxon Nemertodermatida was studied using transmission electron microscopy. Nemertoderma westbladi has paired testes, which are delineated by lining cells. Within each testis, different follicles, each surrounded by a membrane-like structure, are found. Flagellophora apelti has genuinely follicular testes, consisting of several follicles, each containing a certain stage of spermatogenesis. As the gametes are not enclosed by a structure that can be called a true gonad, the structure of the testes differs from most bilaterian animals, but resembles the organization of gametogenic areas of ctenophores. Each stage of spermatogenesis in F. apelti is described, enabling the inference of the origin of the structures seen in mature spermatozoa. The overall structure of the mature spermatozoa is similar in all nemertodermatids and unique within the Metazoa: an elongated head containing the nucleus; a middle piece containing an axoneme, mitochondrial derivatives and in F. apelti granular derivatives; and a flagellar tail.1 aBoone, M.1 aBert, W.1 aClaeys, M.1 aHouthoofd, W.1 aArtois, T.  uhttps://nematodes.myspecies.info/node/84