title: Irineochytrium, a new genus in Chytridiales having zoospores and aplanospores.
abstract: Many described chytrids exhibit distinct morphological features that permit positive identification by light microscopy. Chytriomyces annulatus is one such species. It has a flap-like operculum and its sporangial wall is ornamented with multiple collar-like annulations proximal to the rhizoidal axis, features that, in combination, do not occur in any other described chytrid. Recent molecular phylogenies placed C. annulatus in the Chytridiaceae (Chytridiales) lineage, which is characterized by a Group II zoospore. Here we use light microscopy and transmission electron microscopy to examine thallus morphology of an isolate (JEL 729) of C. annulatus to confirm its identity and transmission electron microscopy to examine zoospore ultrastructure to confirm its phylogenetic placement. Light microscopic examinations confirmed its identity, and transmission electron microscopy analysis revealed both motile spores (zoospores) and nonmotile spores (aplanospores). Zoospores had a unique suite of ultrastructural features characteristic of the Group II zoospore; aplanospores had similar ultrastructure minus a flagellum. Chytriomyces annulatus does not group with the Chytriomycetaceae (Chytridiales) lineage containing the type of Chytriomyces, C. hyalinus, nor does it have a zoospore typical of that lineage. These arguments support the recognition of a distinct genus in Chytridiaceae, including one species, Irineochytrium annulatum.
authors.affiliation: Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama 35487 letch006@bama.ua.edu.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Letcher
authors.affiliation: School of Biology and Ecology, University of Maine, Orono, Maine 04469.
authors.forename: Joyce E
authors.initials: JE
authors.lastname: Longcore
authors.affiliation: Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama 35487.
authors.forename: Martha J
authors.initials: MJ
authors.lastname: Powell
mesh_terms: D008411:Chytridiomycota / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000648:ultrastructure; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D046529:Microscopy, Electron, Transmission; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013172:Spores, Fungal / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification / Q000648:ultrastructure
chemical_list: D004271:DNA, Fungal; D004275:DNA, Ribosomal
keywords: Chytridiomycetes; morphology; systematics; taxonomy; ultrastructure