Garey, J. R.; Campbell, T. G.*: Acanthocephelan and Rotifer Relationships Revisited.

The phylogenetic relationship between Rotifera and Acanthocephala has been a matter of debate for several years. Although these phyla are clearly related, the exact relationship between them had proven difficult to determine with only morphological data. Several phylogenetic analyses based on sequence data have produced trees with Acanthocephala included within Rotifera instead of as a sister phylum. However, the relationship of Acanthocephala to the three classes of Rotifera (Bdelloidea, Seisonidea, Monogononta) has been more difficult to resolve. Some 18S and 16S rDNA studies have shown Acanthocephala to be a sister taxon to Bdelloidea, whereas heat shock protein 82 has placed Acanthocephala as a sister group to a clade composed of both Bdelloidea and Monogononta. A more recent 18S rDNA study showed Acanthocephala as the sister group of Rotifera. Several new 18S sequences for acanthocephalans and monogonont rotifers are now available. We are sequencing the 18S genes from three additional rotifer species: The bdelloids Habrotrocha constrictaand Adineta vaga, and the monogonont floscularid Sinantherina socialis. We present a phylogenetic analysis of the available 18S rotifer and acanthocephalan sequences.