Phylogenetic position of the ciliates Phacodinium (Order Phacodiniida) andProtocruzia (Subclass Protocruziidia) and systematics of the spirotrich ciliates examined by small subunit ribosomal RNA gene sequences

The small subunit rRNA (SSrRNA) genes were sequenced for Protocruzia sp2, P hacodinium metchnicoffi, Holosticha multistylata, and Halteria grandinella. All four genera are placed within the Class Spirotrichea with strong boots trap support in both distance matrix and parsimony tree construction method s and by maximum likelihood analysis using quartet puzzling, Protocruzia sp 2 groups with Protocruzia spl with 100% bootstrap support, and the 5.6% gen etic difference between them strongly argues that they are different specie s although they are morphologically quite similar. The Protocruzia species branch first in the spirotrich clade at a deep level, supporting their reco gnition as a Subclass Protocruziidia. Phacodinium branches after Euplotes a t a deep level, confirming the conclusion that others have reached that thi s genus is related to the hypotrich and stichotrich spirotrichs. Phacodiniu m is assigned to its own family and order, and we conclude that the deep br anching within the spirotrichs argues for its own subclass, the Subclass Ph acodiniidia. Consistent with the partial SSrRNA sequences and with the sequ ence of a polymerase gene, Halteria groups within the stichotrich clade, su pporting the argument that the oligotrichs are not monophyletic as currentl y conceived. Finally, Holo-sticha, which has been assigned to the Order Uro stylida, groups outside the stichotrichs with parsimony analysis, which is consistent with this ordinal assignment, However, it is associated with Hal teria and Oxytricha granulifera in the other analyses. Additional stichotri ch sequences obviously are required before we can confidently begin revisio n of the Subclass Stichotrichia.