The<unk> s are a major assemblage of protists, often known as<unk> .  The phylogenetic category<unk>  contains a variety of free-living and symbiotic forms, and includes some important parasites of humans.  Many<unk> s lack 'classical' mitochondria - these organisms are often referred to as 'amitochondriate', although, most, perhaps all, retain a mitochondrial organelle in greatly modified form. Others have mitochondria with tubular, discoidal, or in some cases, flat cristae.  Most<unk> s 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<unk> s based on genetic evidence (primarily phylogenetic trees of molecular sequences).  Most<unk> s fall into one of four groups, which may be treated as phyla:
Of these, the Percolozoa (Heterolobosea) and Euglenozoa appear to be particularly close relatives, and are united by the presence of discoid cristae within the mitochondria.  Most jakobids have tubular cristae, like most other protists, while the metamonads are unusual in having lost classical mitochondria - instead they have 'hydrogenosomes', 'mitosomes' or uncharacterised organelles.<unk>  relationships are still uncertain; it is possible that they are not a monophyletic group.
Certain<unk> s are often considered among the most primitive eukaryotes, based partly on their placement in many evolutionary trees.  This could encourage proposals that<unk> s are a paraphyletic grade that includes the ancestors of other living eukaryotes.  However, the placement of certain<unk> s as 'early branches' may be an analysis artifact caused by long branch attraction, as has been seen with some other groups, for example, microsporidia.
Excavate
Recluse
Carbromal
Wonder 
Exudate
Wart
Guidewire core
Resection