16 Aug 2002 13:56 AR AR168-MI56-14.tex AR168-MI56-14.SGM LaTeX2e(2002/01/18) P1: GJC 10.1146/annurev.micro.56.012302.160950 Annu. Rev. Microbiol. 2002. 56:315–44 doi: 10.1146/annurev.micro.56.012302.160950 First published online as a Review in Advance on May 7, 2002 THE CLASS MESOMYCETOZOEA: A Heterogeneous Group of Microorganisms at the Animal-Fungal Boundary Leonel Mendoza,1 John W. Taylor,2 and Libero Ajello3 1Medical Technology Program, Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing Michigan, 48824-1030; e-mail:
[email protected] 2Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102; e-mail:
[email protected] 3Centers for Disease Control and Prevention, Mycotic Diseases Branch, Atlanta Georgia 30333; e-mail:
[email protected] Key Words Protista, Protozoa, Neomonada, DRIP, Ichthyosporea ■ Abstract When the enigmatic fish pathogen, the rosette agent, was first found to be closely related to the choanoflagellates, no one anticipated finding a new group of organisms. Subsequently, a new group of microorganisms at the boundary between an- imals and fungi was reported. Several microbes with similar phylogenetic backgrounds were soon added to the group. Interestingly, these microbes had been considered to be fungi or protists. This novel phylogenetic group has been referred to as the DRIP clade (an acronym of the original members: Dermocystidium, rosette agent, Ichthyophonus, and Psorospermium), as the class Ichthyosporea, and more recently as the class Mesomycetozoea. Two orders have been described in the mesomycetozoeans: the Der- mocystida and the Ichthyophonida. So far, all members in the order Dermocystida have been pathogens either of fish (Dermocystidium spp.