Taxonomic Redescriptions of Two Ciliates, Protogastrostyla pulchra n. g., n. comb. and Hemigastrostyla enigmatica (Ciliophora: Spirotrichea, Stichotrichia), with Phylogenetic Analyses Based on 18S and 28S rRNA Gene Sequences

The morphology and infraciliature of two stichotrichid ciliates, Gastrostyla pulchra (Perejaslawzewa 1886) Kahl, 1932 and Hemigastrostyla enigmatica (Dragesco and Dragesco-Kerneis 1986) Song & Wilbert, 1997, collected from marine and brackish sediments, were investigated by using living observations and protargol impregnations. Both 18S and 28S rRNA genes of these two species were sequenced. The 18S rDNA show high similarities (98.4%-99.7%) among populations of each species. There is about 94% similarity in 18S rDNA genes between G. pulchra and Gastrostyla steinii, the type species of the genus, which has been confirmed to be an oxytrichid by previous studies. In the phylogenetic trees of 18S, 28S, and combined 18S and 28S rDNA, both G. pulchra and H. enigmatica are consistently placed outside the well-established oxytrichid clade. Based on our analyses and previous ontogenetic data, we conclude that these two species may represent some lower groups in the subclass Stichotrichia, and that G. pulchra should represent a new genus, Protogastrostyla n. g. This new genus, which is morphologically similar to Gastrostyla, differs in its morphogenesis: the apical part of the old AZM is retained combining with the newly built membranelles that develop from the proter's oral primordium; the primary primordia of the dorsal kinety; and marginal primordia commence de novo without a definite contribution from the old structure.