Molecular phylogeny, taxonomic relationships and North American distribution of <i>Conchophthirus</i> (Conchophthiridae, Scuticociliatia)

<i>Conchophthirus curtus</i> is a scuticociliate found in the mantle cavity of unionid bivalve mussels; it is considered by most to be an endocommensal. It was previously redescribed and its morphogenesis has been carefully defined and evaluated. <i>Conchophthirus</i> stomatogenesis along with its enigmatic deep kinetosomal unit as compared with other scuticociliates, peniculines, and peritrichs suggested possible homologies and affinities. Thus, a comparison of <i>Conchophthirus</i> with common molecular markers to all other ciliates was a goal of this study. We collected <i>Conchophthirus</i> spp. in California from two unionid bivalve hosts: <i>Anodonta californiensis</i> in the Pit River and Lake Merced, and <i>Margaritifera falcata</i> from the Trinity River. The ciliates analyzed were predominantly <i>C. curtus</i> although other conchophthirids were present. The small subunit rRNA and the cytochrome <i>c</i> oxidase subunit 1 genes were sequenced. Phylogenetic analyses of these data were analyzed and maximum likelihood for the small submit rRNA dataset and neighbor-joining for the <i>cytochrome c oxidase subunit 1</i> dataset. The cytochrome c oxidase subunit 1 sequences obtained from <i>M. falcata</i> populations were virtually identical. The analysis placed these sequences with 96% bootstrap support as sister to <i>Dexiotricha</i> sp. The small submit rRNA sequences obtained from populations from both hosts were almost identical, and they showed them to be sister, with 99% support to two unpublished sequences from Chinese populations of <i>Conchophthirus cucumis</i> and <i>C. lamellidens</i>, and sister to a <i>Dexiotricha</i> sp. These data and their analyses confirm <i>Conchophthirus</i> to be a scuticociliate, but not closely related to either philasterine or pleuronematine scuticociliates nor the peniculines or peritrichs. Further analysis awaits additional data. The North American distribution of <i>Conchophthirus</i>, niche analyses, and potential homologous structures are discussed as well as the use of these endocommensals as indicators of water quality and pollution.