Buddenbrockia plumatellae

Buddenbrokia plumatellae is a worm-like parasite of bryozoans whose taxonomic placement long puzzled biologists. It is now classified as one of the only two myxozoans of class Malacosporea on the basis of both genetic and ultrastructural studies. It was the first multicellular myxozoan identified and its vermiform shape initially gave strong support to the theory that the enigmatic group belongs among the Bilateria. Five years later, this was refuted by a study of fifty genes from this same "worm", which had rarely been even seen since its discovery in 1851. These 50 phylogenetic markers reveal that Buddenbrockia is closely related to jellyfish and sea anemones, typical members of a major animal group, the Cnidaria. Because of the fast amino acid replacement rate of the nuclear proteins of Buddenbrockia, as compared to those of the remaining animals sampled in this study, only the use of a sophisticated tree-building approach (i.e., Bayesian inference) allowed to recover its cnidarian evolutionary affinities. One of the researchers talked about the problems encountered studying its morphology: “It has no mouth, no gut, no brain and no nerve cord. It doesn’t have a left or right side or a top or bottom – we can’t even tell which end is the front!” Because the myxozoans are so different from their nearest relatives, he concluded that “the worm-like body shape evolved at least twice from two completely different kinds of animal.”