Some taxonomic and nomenclatural remarks concerning freshwater species of Gastrotricha Chaetonotida are presented. In the family Chaetonotidae, the subgenus Chaetonotus (Hystricochaetonotus) is synonimized with the subgenus C. (Chaetonotus sensu stricto). The genus Lepidochaetus is moved to a subgeneric rank into the genus Chaetonotus, and the subgenus Nudichaetonotus Schwank, 1990 is synonymized with C. (Lepidochaetus). Chaetonotus (Lepidochaetus) brasilianus is proposed as a replacement name for Chaetonotus brasilense Kisielewski, 1991, which has become a secondary junior homonym of Chaetonotus brasiliensis Schwank, 1990. Emended diagnoses of the genus Chaetonotus and of the subgenera C. (Chaetonotus sensu stricto), and Chaetonotus (Lepidochaetus) are given. The 3 subgenera of the genus Ichthydium introduced by Schwank (1990) have not been introduced in the present list. In the family Dasydytidae, the subgenus Dasydytes (Setodytes) is synonymized with the genus Setopus. Six new species by Schwank (1990) (Aspidiophorus ontarionensis, Chaetonotus (C.) furculatus, Chaetonotus (Zonochaeta) annae, Ichthydium malleum, Lepidodermella forficulata and Dasydytes (Setodytes) lemnicola) are nomina nuda. An updated list of the reliable world freshwater species of Gastrotricha is reported.
The spermatozoa of two species supposed to be basal to Gastrotricha Chaetonotida, Neodasys ciritus and Musellifer delamarei, were studied in order to supply further elements to the understanding of sperm evolution in Chaetonotida, a group in which a fully parthenogenetic reproduction is dominant. Two considerably different sperm patterns were found: the spermatozoon of N. ciritus has a simple, conical acrosome, a short, condensed nucleus, few conventional mitochondria randomly arranged along the sperm head, and a 92+2 flagellum perpendicular to the sperm major axis. The spermatozoon of M. delamarei is a filiform cell with a simple acrosome, a partially condensed nucleus, four mitochondria at the nuclear base, and a flagellum with a 92+2 axoneme and large accessory fibers. Some sperm features of M. delamarei are comparable to those of Xenotrichulidae, the only other Chaetonotida producing conventional spermatozoa, whereas the sperm of N. ciritus appears different from all the other patterns known among Gastrotricha, thus knowledge of it does not help in solving the problem of the discussed phylogenetic position of the genus.
The spermatogenesis, the spermiogenetic process and the structure of the mature spermatozoon of Acanthodasys aculeatus (Gastrotricha, Macrodasyida) are described from an ultrastructural point of view. Several spermatogonia in mitotic divisions were seen, proving that euthely of gastrotrichs does not concern gonads. Spermiogenesis is characterized by the early formation of both the acrosome and the axoneme, by the subsequent appearances of a perinuclear helix and of a complex axial tubular structure in the acrosome and by the late development of the peraxonemal striated cylinder. The mature spermatozoon is filiform, and composed of a spiralized acrosome, a helical nuclear–mitochondrial complex and a long flagellum. The acrosome contains an axial tubular structure and the spring‐shaped nucleus delimits a single, long mitochondrion. A perinuclear helix formed by the pro‐acrosome surrounds the nuclear–mitochondrial complex extending for its whole length. A monolayered, obliquely striated cylinder encloses the 9 × 2 + 2 axoneme; its terminal part is empty because of the shortness of the axoneme.
Abstract Guidi, L., Pierboni, L., Ferraguti, M., Todaro, M.A., Balsamo, M. Spermatology of the genus Lepidodasys Remane, 1926 (Gastrotricha, Macrodasyida): towards a revision of the family Lepidodasyidae Remane 1927. -Acta Zoologica (Stockholm) 85 : 211-221The spermatozoa of Lepidodasys unicarenatus and Lepidodasys sp. are filiform and composed of a cork-screw shaped acrosome, a helical nucleus surrounding a mitochondrial axis, and a 9 × 2 + 2 flagellum as in the basic structural model of the macrodasyidan sperm. The genus Lepidodasys has a debated phylogenetic position and has been linked in turn to the family Lepidodasyidae and the family Thaumastodermatidae. The sperm features of the two Lepidodasys species examined are distinct from those typical of the two families: the absence of the periaxonemal cylinder, a character shared only with Turbanellidae among Macrodasyida, could be considered as a symplesiomorphy, suggesting a basal position of the genus along the Macrodasyida clade. Moreover, a comparison of the spermatogenic process of Lepidodasys sp. with those of Acanthodasys aculeatus (Thaumastodermatidae) and Cephalodasys maximus (Lepidodasyidae) has revealed that the process of acrosome formation and nuclear morphology during spermatogenesis are peculiar in Lepidodasys sp. and differences are evident especially in the late stages of spermatogenesis. Penetrated spermatozoa were observed in the oocytes at all maturation stages in L. unicarenatus.
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