PHYLOGENY OF THE NEMERTEAN SUBCLASS PALAEONEMERTEA (ANOPLA, NEMERTEA)

A cladistic analysis based on 50 morphological characters was performe d for 49 of the 98 species currently assigned to the subclass Palaeone mertea (phylum Nemertea), and six additional undescribed species. Thir ty-five species were excluded from the parsimony analysis because of t he high number of unknowns in the character matrix, and one species si nce it was considered a nomen nudum. An initial analysis suggested tha t the subclass Hoplonemertea is the sistergroup to the clade Palaeo- a nd Heteronemertea and the ingroup cladograms are rooted using a paraph yletic outgroup based on this information. Seventy-two equally most pa rsimonious cladograms were found; the consistency index was low but tr ee-length distribution for the character set is skewed to the left, an d the cladograms are invariably shorter than trees based on random dat a. These cladograms suggested a character transformation series for th e cerebral organ where this complex character reappeared several times after being absent. We considered this biologically implausible and t he final discussion is based on three cladograms, one step longer than the most parsimonious, where the evolution of this character appears to be more realistic. The cladistic analysis indicates that many previ ously recognized genera (e.g. Cephalothrix Procephalothrix and Cephalo trichella), and higher taxa, are paraphyletic. It furthermore indicate s that the previously suggested hypothesis of the Archinemertea as a m onophyletic sistertaxon to Palaeonemertea is unsupported. (C) 1994 The Willi Hennig Society.