Abstract
The systematic position of the scuticociliate, Philaster, has been highly ambiguous owing to a lack of either morphogenetic or molecular information. The small subunit rRNA gene of a new species, Philaster apodigitiformis sp. nov. was isolated from eggs of the puffer fish (Takifugu rubripes), was sequenced, and phylogenetic trees were constructed with different methods to assess its position and relationship among the scuticociliates. Results indicate that (1) Philaster apodigitiformis clearly falls into the order Philasterida and it is most closely related to the Uronema-Paranophrys assemblage, which groups with clusters consisting of families Uronematidae, Parauronematidae, Thyrophilacidae and Entorhipidiidae; (2) the two genera Philaster and Philasterides presently assigned to the family Philasteridae are in widely separated clades, indicating that the family is polyphyletic; and (3) the morphological similarity of Philaster and Philasterides is probably an example of evolutionary convergence. The new species P. apodigitiformis is recognised by a combination of the following features: body oval and slightly bilaterally flattened, cilia of paroral membrane conspicuously long and forming a sail-like shape, both membranelle 1 and 2 dominant, and approximately 40 somatic kineties present.