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Related to Myxomycota: Eumycota


see slime moldslime mold
or slime fungus,
a heterotrophic organism once regarded as a fungus but later classified with the Protista. In a recent system of classification based on analysis of nucleic acid (genetic material) sequences, slime molds have been classified in a major group
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Organisms that are classified in the kingdom Fungi and given the class name Myxomycetes, following the rules of botanical nomenclature; or classified in the kingdom Protista at various taxonomic ranks, as class Mycetozoa, following the rules of zoological nomenclature. Evolutionary origins are controversial, but many now believe, based on DNA sequencing techniques, that the Myxomycetes diverge early on the tree of life in the region where other protists are found.

The class consists of 3 subclasses, 6 orders, approximately 57 genera, and 600 species. Subclasses Ceratiomyxomycetidae, Myxogastromycetidae, and Stemonitomycetidae are distinguished by the type of sporophore development, type of plasmodium, and method of bearing spores. The various orders, families, genera, and species are distinguished by characteristics of the fruiting bodies such as spore color, peridium, capillitium, calcium carbonate, or columella.

Myxomycetes begin to appear in May and fruit throughout the summer until October in the north temperate regions. Many species are universally distributed and live in moist and dark places on decaying organic matter. Some species are restricted to more specialized habitats.

Spores are released from the fruiting bodies when disturbed and fall onto the substratum where, when water is present, they germinate and release protoplasts. The protoplasts may develop into either a myxamoeba or a flagellated swarm cell, both of which are haploid and behave like gametes (sex cells). The haploid (monoploid) gametes fuse in pairs forming diploid zygotes, which then divide mitotically without subsequent cell division, resulting in the formation of a multinucleated, free-living mass of unwalled protoplasm called the plasmodium. The diploid plasmodium is representative of the slime stage, and hence the common names sometimes used for this group of organisms include plasmodial, acellular, or true slime molds. The plasmodia ingest food as particulate matter (usually bacteria) by engulfment and are capable of growing to over 70 cm in diameter.

The separate stages in their life cycle make myxomycetes ideal organisms to study basic biological problems, ranging through protoplasmic streaming, the mitotic cycle, morphogenesis, aging, and cell division in cancerous cells. See Eumycota

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.