Genomic insights into the evolutionary origin of Myxozoa within Cnidaria

Myxozoans are a diverse group of microscopic parasites that infect invertebrate and vertebrate hosts. The assertion that myxozoans are highly reduced cnidarians is supported by the presence of polar capsules, which resemble cnidarian stinging structures called "nematocysts." Our study characterizes the genomes and transcriptomes of two distantly related myxozoan species, Kudoa iwatai and Myxobolus cerebralis, and another cnidarian parasite, Polypodium hydriforme. Phylogenomic analyses that use a broad sampling of myxozoan taxa confirm the position of myxozoans within Cnidaria with P. hydriforme as the sister taxon to Myxozoa. Analyses of myxozoan genomes indicate that the transition to the highly reduced body plan was accompanied by massive reduction in genome size, including depletion of genes considered hallmarks of animal multicellularity.