Phylogenetic position of the marine ciliate, Cardiostomatella vermiforme (Kahl, 1928) Corliss, 1960 inferred from the complete SSrRNA gene sequence, with establishment of a new order Loxocephalida n. ord. (Ciliophora, Oligohymenophorea)

The small subunit rRNA (SSrRNA) gene was sequenced for Cardiostomatella vermiforme, a large marine ciliate the systematic position of which is uncertain but which has been regarded as a scuticociliate for about forty years. The present work indicates that this organism, together with a closely related species, Dexiotrichides pangi, always form a separate assemblage as a sister group to the scuticociliates sensu stricto. The fact that the clade comprising Cardiostomatella and Dexiotrichides branches between the typical scuticociliates and Hymenostomatia, and shares a series of morphological and morphogenetical characters with both, supports the conclusion that it belongs to an intermediate group between the two. We suggest that this group represents a new order, Loxocephalida n. ord. within the subclass Scuticociliatia, which possibly contains all taxa within the families Loxocephalidae and Cinetochilidae and with Loxocephalidae as the type family.