PHYLOGENY OF RHABDITIS SUBGENUS CAENORHABDITIS (RHABDITIDAE, NEMATODA)

A phylogenetic analysis was conducted using morphological characters. Eleven of the 18 Caenorhabditis-species described were investigated. T he polarity for character transformations was established and a cladog ram and the character set of the stem species reconstructed. There are two possible positions for R. plicata. It was not possible to resolve the phylogenetic relationship of the Elegans-group, which consists of seven species, including the four best-known Caenorhabditis-species. Transformation series of characters, e.g. the structure of the precloa cal lip, are presented. The evolution of a pharyngeal sleeve is discus sed. For the terms caudal papilla, bursal papilla and ray are given pr ecise definitions. Two individual rays are specified as 'anterior dors al' and 'posterior dorsal'. We present here a new case of a Rhabditis with 10 pairs of bursal papillae where one pair (no. 10) is the phasmi ds. Information on the geographical distribution and the ecology of th e Caenorhabditis-species is given. The markedly different ecological n iches of these Species must be derived from a way of life in the stem species in patchily distributed decomposing organic material which nec essitated a phoretic phase with waving behaviour of the dauer juvenile s.