The Plasmodiophorida and Phagomyxida are orders of zoosporic eukaryotes of
uncertain phylogenetic affinities. We have obtained ribosomal DNA sequence
information from several species in these groups. Phylogenetic analyses of
these sequences have confirmed that they form a monophyletic grouping that
clusters most closely with a rhizopod assemblage consisting of sarcomonads
and chlorarachneans. The Phagomyxida sequences appear distant enough from t
hose of the Plasmodiophorida to justify a separate order. The relationships
between the Plasmodiophorida remain unclear, with species from the same ge
nus showing significant degrees of divergence.