RELATIONSHIP OF HOMOLIDAE AND DROMIIDAE - EVIDENCE FROM SPERMATOZOAL ULTRASTRUCTURE (CRUSTACEA, DECAPODA)

The homolid spermatozoon, as exemplified by Homola sp., Paromola sp. a nd Paromola petterdi, differs markedly from spermatozoa of crabs of th e Heterotremata-Thoracotremata assemblage but agrees with the sperm of dromiids, in the strongly anteroposteriorly depressed acrosome (apomo rphy?) and the capitate form of the perforatorium (a major synapomorph y seen nowhere else in the Crustacea). These similarities support incl usion of the Dromiidae and Homolidae in a single grouping, the Podotre mata. The homolid perforatorium differs from that of dromiids in the a utapomorphic spiked-wheel form of the anterior expansion. Homolid sper matozoa show nuclear arms symplesiomorphic of all investigated crabs ( small or questionably sometimes absent in Dromiidae), and correspondin g loss of purely microtubular arms seen in other reptants. Homolid spe rm agree with those of dromiids (synapomorphy?), raninids, higher hete rotremes and thoracotremes (homoplasies?) but differ from lower hetero tremes, in lacking microtubules in the nuclear arms. A posterior media n process of the nucleus in homolids, not seen in dromiids, is shared with anomurans and lower heterotremes. No features in the ultrastructu re of homolid or dromiid sperm have been detected which associate them exclusively with either the Raninidae or the heterotreme and thoracot reme Brachyura.