A Molecular and Ultrastructural Description of S pathidiopsis buddenbrocki and the Phylogenetic Position of the Family Placidae ( Ciliophora).

ABSTRACT S pathidiopsis and P lacus are the only two genera within the family Placidae. The family has been placed in the class Prostomatea and order Prorodontida because its members have somatic monokinetids with a radial transverse ribbon, a straight non-overlapping postciliary ribbon, and anteriorly directed non-overlapping kinetodesmal fibril, an apical cytostome lacking specialized oral cilia, a brosse, and toxicysts. To confirm the stability of this placement, ultrastructural morphology and small subunit rRNA gene sequences of S pathidiopsis socialis, S pathidiopsis buddenbrocki, and P lacus striatus were determined. These data were combined with information from other ciliates, and phylogenetic trees were generated using maximum-likelihood and maximum-parsimony methods. The analyses confirmed the family Placidae to be a monophyletic group in the Prostomatea with the Placidae a sister group to a C ryptocaryon + C oleps + P rorodon clade. [ABSTRACT FROM AUTHOR]