Ultrastructure of spermiogenesis and spermatozoa in the platyhelminthsActinodactylella blanchardi(Temnocephalida, Actinodactylellidae),Didymorchissp. (Temnocephalida, Didymorchidae) andGieysztoriusp. (Dalyelliida, Dalyelliidae), with implications for the phylogeny of the Rhabdocoela

Abstract

Summary Spermiogenesis and mature sperm in the two temnocephalids Actinodactylella blanchardi and Didymorchis sp. closely resemble those observed in six other temnocephalids reported in the preceeding paper. A dense heel region forms at the base of each basal body, the intercentriolar body splits into two halves, and rotation of the flagellar anchoring apparatus causes compression of one of the two rows of microtubules that lined the zone of differentiation. A region of spiral microtubules in the spermatozoon proximal to the flagellar insertion zone results from the gradual and uneven expansion of the compressed inner row of microtubules. By contrast, in the dalyelliid Gieysztoria sp. the inner compressed row expands evenly and over a very short distance so that no region of spirally arranged microtubules occurs. In both the temnocephalids the proximal end of the spermatozoon terminates after splitting into a number of fine processes containing microtubules, while the dalyelliid terminates with a simple t...