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Chytridiomycota
Chytridiomycota is a phylum in the kingdom Fungi. The name is derived from the Greek ''chytridion'', meaning "little pot", describing the structure containing unreleased zoospores. In older classifications, chytrids (except the recently established order Spizellomycetales) were placed in the class Phycomycetes under the subphylum Myxomycophyta of the kingdom Fungi. Previously, they were placed in the Mastigomycotina as the class Chytridiomycetes.〔The Fungi: An Advanced Treatise Vol IVB A Taxonomic Review with Keys: Basidiomycetes and Lower Fungi. 1973. Edited by Ainsworth, Sparrow & Sussman. Academic Press: New York.〕 Also, in an older and more restricted sense (not used here), the term "chytrids" referred just to those fungi in the order Chytridiales. Here, the term “chytrid” will refer only to members of Chytridiomycota.〔Alexopoulos CJ, Mims CW, Blackwell M. 1996. Introductory Mycology. 4th edition. John Wiley & Sons, Inc.〕 The chytrids have also been included among the Protoctista,〔 but are now regularly classed as fungi. Chytrids are one of the early diverging fungal lineages and are saprobic, degrading refractory materials such as chitin and keratin, or acting as parasites.〔Sparrow FK. 1960. Aquatic Phycomyetes. The University of Michigan Press:Ann Arbor. 2nd edition〕 Their membership in kingdom Fungi is demonstrated with chitin cell walls, a posterior whiplash flagellum, absorptive nutrition, use of glycogen as an energy storage compound, and synthesis of lysine by the α-amino adipic acid (AAA) pathway.〔〔Kendrick, Bryce. 2000. The Fifth Kingdom. 3rd edition Focus Publishing: Newburyport, MA.〕 There are approximately over 750 chytrid species distributed among 7 orders.〔http://bama.ua.edu/~nsfpeet/〕 There has been a significant increase in the research of chytrids since the discovery of ''Batrachochytrium dendrobatidis'', the causal agent of chytridiomycosis.〔Blackwell M. 2011. The Fungi: 1,2,3 … million species? American Journal of Botany 98:426-438.〕〔Longcore JE, AP Pessier & DK Nichols. 1999. Batrachochytirum dendrobatidis gen. et sp. nov., a chytrid pathogenic to amphibians. Mycologia 91(2):219-227.〕
==Life cycle & body plan==
Chytridiomycota are unusual among the Fungi in that they reproduce with zoospores.〔〔Hibbett et al. 2007. A higher-level phylogenetic classification of the Fungi. Mycologia 111(5): 509-547.〕 For most members of Chytridiomycetes, sexual reproduction is not known. Asexual reproduction occurs through the release of zoospores (presumably) derived through mitosis.〔 Where it has been described, sexual reproduction of Chytridomycetes occurs via a variety of methods. It is generally accepted that the resulting zygote forms a resting spore, which functions as a means of surviving adverse conditions.〔 In some members, sexual reproduction is achieved through the fusion of isogametes (gametes of the same size and shape). This group includes the notable plant pathogens ''Synchytrium''. Some algal parasites practice oogamy: a motile male gamete attaches itself to a nonmotile structure containing the female gamete. In another group, two thalli produce tubes that fuse and allow the gametes to meet and fuse.〔 In the last group, rhizoids of compatible strains meet and fuse. Both nuclei migrate out of the zoosporangium and into the conjoined rhizoids where they fuse. The resulting zygote germinates into a resting spore.〔 Sexual reproduction is common and well known among members of the Monblepharidomycetes. Typically, these chytrids practice a version of oogamy: the male is motile and the female is stationary. This is the first occurrence of oogamy in kingdom Fungi.〔 Briefly, the monoblephs form oogonia, which give rise to eggs, and antheridia, which give rise to male gametes. Once fertilized, the zygote either becomes an encysted or motile oospore,〔 which ultimately becomes a resting spore that will later germinate and give rise to new zoosporangia.〔 Upon release from the germinated resting spore, zoospores seek out a suitable substrate for growth using chemotaxis or phototaxis. Some species encyst and germinate directly upon the substrate; others encyst and germinate a short distance away. Once germinated, enzymes released from the zoospore begin to break down the substrate and utilize it produce a new thallus. Thalli are coenocytic and usually form no true mycelium (having rhizoids instead). Chytrids have several different growth patterns. Some are holocarpic, which means they only produce a zoosporangium and zoospores. Others are eucarpic, meaning they produce other structures, such as rhizoids, in addition to the zoosporangium and zoospores. Some chytrids are monocentric, meaning a single zoospore gives rise to a single zoosporangium. Others are polycentric, meaning one zoospore gives rise to many zoosporangium connected by a rhizomycelium. Rhizoids do not have nuclei while a rhizomycelium can.〔 Growth continues until a new batch of zoospores are ready for release. Chytrids have a diverse set of release mechanisms that can be grouped into the broad categories of operculate or inoperculate. Operculate discharge involves the complete or incomplete detachment of a lid-like structure, called an operculum, allowing the zoospores out of the sporangium. Inoperculate chytrids release their zoospores through pores, slits, or papillae.〔
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