Invertebrate zoologists consider the phyla Dicyemida, Orthonectida
, Placozoa, Cycliophora, Entoprocta (Kamptozoa), Chaetognatha, Pterobranchia, and Enteropneusta along with the order Seisonidae.
The spiral cleavage, musculature (Slyusarev and Starunov, 2016), and fine structure of ciliated cells and ciliary rootlets (Slyusarev and Kristensen, 2003) of Orthonectida show similarities to those of annelids; therefore, it has been suggested that they be a member of the Protostomia.
There are four reported genera for the phylum Orthonectida: Rhopalura, Intoshia, Ciliocincta, and Stoecharthrum.
nov., that parasitizes xenoturbellids, thus revealing that there is still hidden diversity within the phylum Orthonectida. Biological surveys of previously uninvestigated environments, such as the deep sea and the polar regions, and research on various non-model organisms are now becoming prominent.
Classe des Orthonectides (Orthonectida Giard 1877).
A new ophiuroid host for Rhopalura ophiocomae Giard (Orthonectida: Mesozoa).
Sur les Orthonectida, classe nouvelle d'animaux parasites des echinodermes et des turbellaries.
The Orthonectida, a new class of the phylum of the worms.
The phylogenetic position of Rhopalura ophiocomae (Orthonectida) based on 18S ribosomal DNA sequence analysis.
Three new species of Stoecharthrum (phylum Orthonectida).
Molecular analyses that include other lower turbellarian groups (for example, the Catenulida and the Nemertodermatida) and the Orthonectida
, a group tentatively included in the Mesozoa, will provide further information for understanding the phylogenetic position of the dicyemids.