Morphology, taxonomy and molecular phylogeny of three marine peritrich ciliates, including two new species: Zoothamnium apoarbuscula n. sp. and Z. apohentscheli n. sp. (Protozoa, Ciliophora, Peritrichia)

Zoothamnium is a speciose genus, most species of which have incomplete morphological data based on modern criteria. In the present study, the morphology of three species of Zoothamnium, i.e., Z. apoarbuscula n. sp., Z. apohentscheli n. sp., and Z. alternans, collected in Qingdao, China, was revealed using living observation and silver staining. In addition, the SSU rDNA of each species was sequenced for phylogenetic analyses. Zoothamnium apoarbuscula n. sp. is characterized by its umbellate colony which is up to 900 μm high, dichotomously branched stalk, differentiation of zooids, and infundibular polykinety 3 comprising three equal-length ciliary rows. Zoothamnium apohentscheli n. sp is characterized by its large colony up to 1700 μm high, alternately branched stalk, and infundibular polykinety 3 comprising three equal-length ciliary rows. A population of Z. alternans is described in detail. Phylogenetic analyses based on SSU rDNA sequence data revealed that species with an alternately branched stalk cluster together in gene trees and probably represent an independent lineage within the genus Zoothamnium.