ABSTRACT
Coccidians fall within Class Sporozoea Leuckart 1879 and are the largest Subclass within the apicomplexans, containing around 2300 named species. They are further classified within the Order Eucoccidiida, which has two suborders: Adeleorina Leger 1911 and Eimeriorina Leger 1911. Since the 1990s, researchers have increasingly incorporated molecular phylogenetics to investigate divisions within the Eimeriorina, inferring descent relationships by reconstructing the history of changes in homologous DNA sequences. Most extant molecular phylogenetic studies of the organisms have relied exclusively on variation in the ribosomal DNA small subunit 18S locus. It has been the workhorse of phylogenetic studies, because structural constraints define highly conserved regions of the molecule that are interspersed by more variable regions that record changes capable of diagnosing groups of taxa sharing especially close common ancestry. Fewer than 10% of the 1500 named species of Eimeria are represented in any published phylogeny.
