HUFF, Stephanie; LIPSCOMB, Diana: The Phylogenetic Position of Karyorelictid Ciliates (Phylum Ciliophora)

Karyorelictid ciliates are very common in marine littoral sands. Like all ciliates, they have two kinds of nuclei (a macronucleus for most protein transcription and micronucleus which functions in genetic transmission), rows of cilia with a distinctive infraciliature (transverse and postciliary microtubules and a kinetodesmal fiber), a permanent cell mouth or cytostome, and transverse cell division. Unlike other ciliates, the macronucleus is nondividing and diploid (rather than polyploid) and the cytostome is not surrounded by complex feeding cilia. Thus, some protistologists consider the karyorelictids to be primitive ciliates. However, the infraciliature of karyorelictids is identical to that of heterotrichs which, because they have polyploid macronuclei and adoral complexes of cilia around the cytostome, are considered among the most advanced ciliates. Therefore, other protozoologists hypothesize that they are derived ciliates that have secondarily simplified their nuclei and oral cilia. Recently, analysis of small subunit RNA sequences of a few karyorelictids united Karyorelictida and Heterotrichida but place them both at the base of the ciliate tree, indicating that ciliate evolution has proceeded by simplification from the complex structures seen in heterotrichs to those found in other classes. To test these hypotheses we have reanalyzed molecular and morphological data to which we have added sequence information from karyorelictids in the genus Gelia, Trachelocerca, Tracheloraphis, and Alveola as well as additional sequences of heterotrichs. In addition to presenting these results, the impact of problems with sequence alignment on resolving the phylogenetic position of the karyorelictids will be discussed.