New sperm types in Naididae and Lumbriculidae (Annelida: Oligochaeta) and their possible phylogenetic implications

The sperm ultrastructure of three Naididae ( Paranais frici, P. litoralis and Stylaria lacustris) and two Lumbriculidae (Rhynchelmis brachycephala and R. alyonae) is decribed to supply spermatological evidence towards a better understanding of the phylogeny of the two families. Naidid spermatozoa were found to be similar to one another, particularly with regard to the acrosome (with the acrosome tube bent to one side), and the shape and number of mitochondria. The various morphological characters do not militate against the previously proposed inclusion of naidids within the Tubificidae. The two lumbriculid species examined showed a characteristic conical indentation at the apex of the nucleus, a feature up to now described only in Branchiobdellida, an annelid group with possible affinities to Lumbriculidae.