Cladistic analysis of myxozoan species with known alternating life-cycles.

The phylogenetic relationships of 15 myxozoan taxa with known alternating life-cycles were investigated in order to provide insight into the puzzling matches between myxosporeans and actinosporeans of the myxozoan life-cycle data. Phylogenetic analyses were performed using two partitioned data-sets of life-cycle stages, myxosporean stage from fish hosts versus actinosporean stage from annelid hosts, and a combined data-set of myxosporean and actinosporean stages. A cnidarian parasite of fish, Polypodium hydriforme Ussov, 1885, was used as the outgroup. The supraspecific level grouping in the conventional classification of actinosporeans was not supported in the analysis of the partitioned data from the actinosporean phase, which yielded two equally parsimonious trees. Analysis of the partitioned data from the myxosporean phase provided 24 equally parsimonious trees and did not support the current classification of myxosporeans. The analyses of the partitioned data of myxozoans by life-cycle stage revealed a lack of taxonomic congruence between the two life-stage partitions. Two equally parsimonious trees were obtained from analysis of the combined data. The suborder Variisporina of the Myxozoa was not supported by the total evidence trees, while the monophyly of the species of Myxobolus Butschli, 1882 and of the Myxidiidae were supported. The cladograms from the combined data revealed that these myxozoan species formed four major monophyletic groups. Among them, two were supported by the partitioned data of the actinosporean phase. The phylogenetic signals and the better resolution reflected by the trees of combined data suggest that the phylogenetic total evidence approach should be employed in future studies of the systematics of myxozoans.