THE PHYLOGENETIC POSITION OF UDONELLA (PLATYHELMINTHES)

Phylogenetic analysis of molecular data from complete 18S rRNA and par tial 28S rRNA genes, of a variety of platyhelminths, places the enigma tic Udonella caligorum firmly as a monopisthocotylean monogenean. Both maximum parsimony and a modified distance measure, operating under a maximum likelihood model, gave identical solutions for each data set. These data further support morphological evidence from ultrastructural studies indicating the neodermatan affinities of Udonella, namely sha red features in sensory receptors, surface tegument, sperm structure a nd spermiogenesis. The molecular data reject the class Udonellidea and the placement of udonellids as sister-group to the Neodermata. As sho wn previously with molecular data, the monogeneans appear as a paraphy letic assemblage comprising strongly monophyletic Monopisthocotylea an d Polyopisthocotylea. Their relationships with the trematodes and cest odes are not resolved with 28S rDNA or 18S rDNA alone. (C) 1998 Austra lian Society for Parasitology. Published by Elsevier Science Ltd.