Molecular phylogenetic analysis of the coccidian cephalopod parasites Aggregata octopiana and Aggregata eberthi (Apicomplexa: Aggregatidae) from the NE Atlantic coast using 18S rRNA sequences

The coccidia genus Aggregata is responsible for intestinal coccidiosis in wild and cultivated cephalopods. Two coccidia species, Aggregata octopiana, (infecting the common octopus Octopus vulgaris), and A. eberthi, (infecting the cuttlefish Sepia officinalis), are identified in European waters. Extensive investigation of their morphology resulted in a redescription of A. octopiana in octopuses from the NE Atlantic Coast (NW Spain) thus clarifying confusing descriptions recorded in the past. The present study sequenced the 18S rRNA gene in A. octopiana and A. eberthi from the NE Atlantic coast in order to assess their taxonomic and phylogenetic status. Phylogenetic analyses revealed conspecific genetic differences (2.5%) in 18S rRNA sequences between A. eberthi from the Ria of Vigo (NW Spain) and the Adriatic Sea. Larger congeneric differences (15.9%) were observed between A. octopiana samples from the same two areas, which suggest the existence of two species. Based on previous morphological evidence, host specificity data, and new molecular phylogenetic analyses, we suggest that A. octopiana from the Ria of Vigo is the valid type species.