Phylogenetic analysis of the small subunit ribosomal RNA of Marteilia refringens validates the existence of phylum paramyxea (Desportes and Perkins, 1990)

Marteilia refringens is recognized as one of the most significant pathogens of bivalve molluscs. The nucleotide sequence of the small subunit ribosoma l RNA gene of Marteilia refringens is used to elucidate the phylogenetic po sition of the phylum Paramyxea. Genomic DNA was extracted from sporangia of Marteilia, purified from infected blue mussels, Mytilus edulis, and flat o ysters, Ostrea edulis. The sequences obtained from Marteilia species purifi ed from both oysters and mussels were identical. The sequence identity was confirmed by in situ hybridization using a DNA probe targeted to a variable region of the ribosomal DNA. The small subunit ribosomal RNA gene sequence of M. refringens is very different from all known sequences of eukaryotic organisms, including those of myxosporeans and haplosporeans. Therefore. th e phylum Paramyxea should continue to be recognized as an independent eukar yotic phylum.