Entamoebid
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{{Taxobox
| color = khaki
| name = Entamoebids
| regnum = Protista
| phylum = Amoebozoa
| ordo = Entamoebida
| subdivision_ranks = Species
| subdivision =
Entamoeba coli
Entamoeba histolytica
Entamoeba invadens
Endolimax nana
etc.
}}
The entamoebids or entamoebae are a group of amoebozoa found as internal parasites or commensals of animals. The cells are uninucleate small, typically 10-100 μm across, and usually have a single lobose pseudopod taking the form of a clear anterior bulge. There are two major genera, Entamoeba and Endolimax. They include several species that are pathogenic in humans, most notably Entamoeba histolytica, which causes amoebic dysentery.
Entamoebids lack mitochondria. This is a secondary loss, possibly associated with their parasitic life-cycle. Studies show they are close relatives of the pelobionts, another group of amitochondriate amoebae, but unlike them entamoebids retain dictyosomes. Both groups are now placed alongside other lobose amoebae in the phylum Amoebozoa.
Studying Entamoeba invadens, David Biron of the Weizmann Institute of Science and coworkers found that about one third of the cells are unable to separate unaided and recruit a neighboring amoeba (dubbed the "midwife") to complete the fission. He writes:
- When an amoeba divides, the two daughter cells stay attached by a tubular tether which remains intact unless mechanically severed. If called upon, the neighbouring amoeba midwife travels up to 200 μm towards the dividing amoeba, usually advancing in a straight trajectory with an average velocity of about 0.5 μm/s. The midwife then proceeds to rupture the connection, after which all three amoebae move on.
They also reported a similar behavior in Dictyostelium.