Sperm morphology in Serpulorbis and Dendropoma and its relevance to the systematic position of the vermetidae (gastropoda)

Abstract

Electron microscopic observations on the euspermatozoa (fertilizing sperm) and paraspermatozoa (infertile sperm) of Serpulorbis sp. and Dendropoma sp. suggest that the family Vennetidae (sensu stricto) is not closely allied to any true cerithioidean family. Vermetid euspermatozoa strongly resemble those of a number of other mesogastropod superfamilies including the Stromboidea, Epitonioidea, Naticoidea, Calyptraeoidea, Cypraeoidea, some rissooideans and littorinoideans, and even some neogastropod taxa. Vermetid paraspermatozoa are anudeate, with one or more tails extending from both ends of a central body region. In contrast, paraspermatozoa of true cerithioideans: (1) have tails extending from only the posterior region of the 'head' (2) usually retain a condensed nuclear remnant and (3) sometimes possess an acrosome-like structure at the head apex. These results, in conjunction with anatomical work by Morton, suggest that the Vennetidae should be removed from the Cerithioidea and placed probably in its own superfamily (Vermetoidea Raphinesque, 1815) as practised by some recent workers. The Vermetoidea possibly are associable with the Stromboidea/Calyptraeoidea/Hipponicoidea/Xeno-phoroidea block within the Mesogastropoda © 1988 The Malacological Society of London.