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Excavate
The excavates are a major subgroup of unicellular eukaryotes, often known as Excavata. The phylogenetic category Excavata, proposed by Cavalier-Smith in 2002, contains a variety of free-living and symbiotic forms, and also includes some important parasites of humans. Excavates were formerly considered to be included in the now obsolete Protista kingdom.
==Characteristics==
Many excavates lack 'classical' mitochondria - these organisms are often referred to as 'amitochondriate', although most, perhaps all, retain a mitochondrial organelle in greatly modified form (e.g. a hydrogenosome or mitosome). Among those with mitochondria, the mitochondrial cristae may be tubular, discoidal, or in some cases, laminar. Most excavates have two, four, or more flagella and many have a conspicuous ventral feeding groove with a characteristic ultrastructure, supported by microtubules. However, various groups that lack these traits may be considered excavates based on genetic evidence (primarily phylogenetic trees of molecular sequences).
The closest that the excavates come to multicellularity are the Acrasidae slime molds. Like other cellular slime molds, they live most of their life as single cells, but will sometimes assemble into a larger cluster.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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