Linking multi-gene and morphological data in the subclass Scuticociliatia (Protista, Ciliophora) with establishment of the new family Homalogastridae fam. nov.

Scuticociliatia is one of the most species-rich subclasses in the phylum Ciliophora. The evolutionary relationships among Scuticociliatia groups have long been very unclear due to the homogeneity of morphology and insufficiency of molecular data. With morphological and multi-gene-based molecular data presented here, the evolutionary phylogeny of several Scuticociliatia taxa that were hitherto especially poorly defined is analyzed and discussed. The results indicate: (1) all scuticociliates cluster into two well supported and one poorly supported group, representing three order-level taxa; (2) with the support of both morphological and molecular data, a new family Homalogastridae fam. nov. is proposed in the order Philasterida; (3) Parauronema is formally transferred to Uronematidae and Potomacus is treated as incertae sedis in the order Philasterida, therefore Parauronematidae is proposed to be a junior synonym of Uronematidae; (4) the genus Madsenia and the species Parauronema longum and Pseudocyclidium longum are treated as incertae sedis, while the genus Protophyra should be maintained in the family Ancistridae. In addition, the putative secondary structure of internal transcribed spacer 2 (ITS2) of representative taxa from the three orders of Scuticociliatia are analyzed, and consensus structures and nucleotide composition in each order are exhibited.