| Abstract: | The small subunit rRNA (SSrRNA) genes of six marine oligohymenophoreans, namely Uronemella filificum , Schizocalyptra sp.-WYG07060701, Schizocalyptra aeschtae , Pleuronema sinica , P. czapikae and Paratetrahymena sp., were sequenced. Phylogenetic trees were constructed with four different methods to assess the inter- and intrageneric relationships among the scuticociliates and the phylogenetic assignment of the order Loxocephalida. The SSrRNA phylogeny indicates that: (i) Paratetrahymena is most closely related to Cardiostomatella ; (ii) the order Loxocephalida and the family Uronematidae both appear to be polyphyletic; (iii) the order Philasterida is a well-defined taxon; (iv) Cyclidium porcatum falls outside the order Pleuronematida in all analyses; (v) the validity of the genus Uronemella is confirmed; (vi) Schizocalyptra is a member of the family Pleuronematidae. Furthermore, the predicted secondary structures of the variable region 4 of the SSrRNA gene sequences show that the size of the terminal bulge in Helix E23–7 is probably different for the orders Philasterida and Pleuronematida. Also, compared to Uronema and Homalogastra , Uronemella has distinct patterns in Helices E23–1, E23–7, E23–8 and E23–9. |
