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Ultrastructural studies of spermatozoa in three bivalve species with notes on evolution of elongated sperm nucleus in primitive spermatozoa
A comparison of sperm ultrastructure among bivalves indicates that there is a certain correlation between the evolution of the elongated sperm nucleus and large, yolk-rich eggs. Expand
The ciliated epidermis of Xenoturbella bocki (Platyhelminthes, Xenoturbellida) with some phylogenetic considerations
The epidermis of Xenoturbella bocki Westblad was studied by scanning and transmission electron microscopy and showed a characteristic pattern of axonemal filament termination in the distal tips of their cilia, which may be an apomorphic feature which indicates a close relationship between xenoturbellida, Nemertoder‐matida and Acoela. Expand
Ultrastructure of spermatozoa and spermiogenesis in the hydrozoan Cordylophora caspia with comments on structure and evolution of the sperm in the Cnidaria and the Porifera
Spermiogenesis in the hydroid, Cordylophora caspia, illustrates many of the features of this process in cnidarians and those of primitive sperm structure in primitive metazoans and supports the suggestion of Afzelius (1972) that the sperm in the Porifera has arisen independently of the primitive sperm inThe Cnidaria. Expand
Ultrastructure of multiciliated collar cells in the pilidium larva of Lineus bilineatus (Nemertini)
The ultrastructure of the apical plate of the free-swimming pilidium larva of Lineus bilineatus is described with particular reference to the multiciliated collar cells, which are rather simple and unspecialized. Expand
Spermiogenesis and ultrastructure of spermatozoa in Saxipendium coronatum (Hemichordata, Enteropneusta), with consideration of their relation to reproduction and dispersal
The sperm of Saxipendium and the small eggs found in the female suggest non-specialized external fertilization and embryogeny leading to a planktotrophic larva. Expand
The spermatozoon of the jellyfish Nausithoë.
The spermatozoon of the primitive scyphomedusa Nausithoe has a short conical head, a midpiece containing four large mitochondria, and a long tail consisting of a flagellum. It is therefore aExpand
The Spermatozoon of Gononemertes parasita Nemertea, (Hoplonemertea) With a Note on Sperm Evolution in the Nemerteans
Summary The spermatozoon of the nemertean Gononemertes parasita has been examined using electron microscopy. The spermatozoon is of a modified type with an elongated, approximately rod-shaped nucleusExpand
The Spermatozoon of Siboglinum (Pogonophora)
It is concluded that the ancestral form must have had a fairly primitive spermatozoon and that evolution has proceeded towards a modified sperm with complicated spiral structure in connection with the evolution of a modified biology of fertilization, viz. specialized spermatophores. Expand