excavata excavata excavata is a former supergroup of unicellular organisms belonging to the domain eukaryota. it was first suggested by simpson and patterson in 1999 and introduced by thomas cavalier-smith in 2002 as a formal taxon. it contains a variety of free-living and symbiotic forms, and includes some important parasites of humans, such as giardia and trichomonas. excavates were formerly considered to be included in the now obsolete protista kingdom. they were classified based on their flagellar structures, and were considered to be the most basal flagellate lineage. excavatatemporal range: giardia lamblia, a parasitic diplomonad scientific classification (obsolete as paraphyletic) domain: eukaryota (unranked): excavata(cavalier-smith), 2002 phyla and classes see text three types of excavate cells. top: jakobida, 1-nucleus, 2-anterior flagellum, 3-ventral/posterior flagellum, 4-ventral feeding groove. middle: euglenozoa, 1-nucleus, 2-flagellar pocket/reservoir, 3-dorsal/anterior flagellum, 4-ventral/posterior flagellum, 5-cytostome/feeding apparatus. bottom: metamonada, 1-anterior flagella, 2-parabasal body, 3-undulating membrane, 4-posterior flagellum, 5-nucleus, 6-axostyle. phylogenomic analyses indicate that the excavata are polyphyletic, not forming a single natural group. excavata has therefore been split into three groups, not all closely related: discobids, metamonads and malawimonads. except for euglenozoa, they are all non-photosynthetic. characteristics most excavates are unicellular, heterotrophic flagellates. only the euglenozoa are photosynthetic. in some (particularly anaerobic intestinal parasites), the mitochondria have been greatly reduced. some excavates lack "classical" mitochondria, and are called "amitochondriate", although most 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. many have a conspicuous ventral feeding groove with a characteristic ultrastructure, supported by microtubules—the "excavated" appearance of this groove giving the organisms their name. however, various groups that lack these traits may be considered excavates based on genetic evidence (primarily phylogenetic trees of molecular sequences). the acrasidae slime molds are the only excavates to exhibit limited multicellularity. like other cellular slime molds, they live most of their life as single cells, but will sometimes assemble into larger clusters. proposed group