CLASS-LEVEL RELATIONSHIPS IN THE PHYLUM CNIDARIA - MOLECULAR AND MORPHOLOGICAL EVIDENCE

The evolutionary history of cnidarian life cycles has been debated sin ce the 1880s, with different hypotheses favored even by current textbo oks. Contributing to the disagreement is the fact that the systematic relationships of the four cnidarian classes have received relatively l ittle examination using modern systematic methods. Here we present ana lyses of class-level relationships based on 18S ribosomal DNA (rDNA) s equence, mitochondrial 16S rDNA sequence, mitochondrial genome structu re, and morphological characters. DNA sequences were aligned using a r epeatable parsimony-based approach incorporating a range of alignment parameters. Analyses of individual data sets and of ail data combined are unanimous in grouping the classes possessing a medusa stage, leavi ng the holobenthic Anthozoa basal within the phylum.