Cryptosporidium is more closely related to the gregarines than to coccidiaas shown by phylogenetic analysis of apicomplexan parasites inferred usingsmall-subunit ribosomal RNA gene sequences

The phylogenetic placement of gregarine parasites (Apicomplexa: Gregarinasi na) within the Apicomplexa was derived by comparison of small-subunit ribos omal RNA gene sequences. Gregarine sequences were obtained from Gregarina n iphandrodes Clopton, Percival, and Janovy, 1991, and Monocystis agilis Stei n, 1848 (Eugregarinorida Leger 1900), as well as from Ophriocystis elektros cirrha McLaughlin and Myers, 1970 (Neogregarinorida Grasse 1953). The seque nces were aligned with several other gregarine and apicomplexan sequences f rom GenBank and the resulting data matrix analyzed by parsimony and maximum -likelihood methods. The gregarines form a monophyletic clade that is a sis ter group to Cryptosporidium spp. The gregarine/ Cryptosporidium clade is s eparate from the other major apicomplexan clade containing the coccidia, ad eleids, piroplasms, and haemosporinids. The trees indicate that the genus C ryptosporidium has a closer phylogenetic affinity with the gregarines than with the coccidia. These results do not support the present classification of the Cryptosporidiidae in the suborder Eimerioirina Leger, 1911.