TY - JOUR T1 - Spermatogenesis and the structure of the testes in Nemertodermatida JF - ZoomorphologyZoomorphology Y1 - 2011 A1 - Boone, M. A1 - Bert, W. A1 - Claeys, M. A1 - Houthoofd, W. A1 - Artois, T. SP - 273 EP - 282 AB - The 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. VL - 130 SN - 0720-213X N1 - Boone, Mieke Bert, Wim Claeys, Myriam Houthoofd, Wouter Artois, Tom ER -