The pelobionts are a small group of amoebae that lack mitochondria. The most notable member is Pelomyxa, called giant amoebae because they reach sizes of up to 3 mm. They also include the flagellated amoebae Mastigamoeba, Mastigella, and Mastigina. Both pelobionts and the closely related entamoebae lack mitochondria and dictyosomes, now known to be a secondary absence. They are now included in the phylum Amoebozoa.
The most notable member is Pelomyxa pelustris, called the giant amoeba because of its size: usually 500-800 μm, but occasionally passing 3 mm in length.
The other pelobionts are monoflagellate amoebae, which share various ultrastructural characteristics with Pelomyxa.
The group does not appear to have any other especially close relatives, and probably diverged from the other eukaryotes early on.
Both pelobionts and the closely related entamoebae lack mitochondria and dictyosomes, now known to be a secondary absence.
The mitochondria characteristically have branching tubular cristae, but have been lost among pelobionts and the parasitic entamoebids, collectively referred to as archamoebae based on the earlier assumption that the absence was primitive.
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