Phylogenetic analysis of the rumen ciliate family Ophryoscolecidae based on 18S ribosomal RNA sequences, with new sequences from Diplodinium, Eudiplodinium, and Ophryoscolex

Phylogenetic relationships within the largest family of entodiniomorphid rumen ciliates, the Ophryoscolecidae, were inferred from comparisons of small-subunit ribosomal RNA gene sequences. These included three new sequences from Diplodinium dentatum (1638 base pairs (bp)), Eudiplodinium maggii (1637 bp), and Ophryoscolex purkynjei (1636 bp). Using morphological characters, Lubinsky constructed a cladogram of the Ophryoscolecidae, and on the basis of his analysis, he divided the family into three subfamilies (Entodiniinae, Diplodiniinae, Ophryoscolecinae) to reflect his ''natural'' groupings (G. Lubinsky. 1957. Can. J. Zool. 35: 141-159). Our cladistic analysis, based on the limited morphological and ultrastructural data available, indicates that there are no synapomorphies supporting the Diplodiniinae sensu Lubinsky. However, based upon the six 18S sequences for the Ophryoscolecidae, the rumen ciliates are monophyletic and fall into three distinct groups corresponding to Lubinsky's subfamilial division of the family. Our molecular analysis shows Entodinium to be the earliest branching rumen ciliate (subfamily Entodiniinae) and Eudiplodinium, not Diplodiium, branching first among the diplodiniines.