Blobby amoebae are closer kin to you than plants are
Amoebozoa, a supergroup of about 2,400 described species, includes classroom amoebae, parasites and slime moulds that can spread across several square metres. Genetic trees place it as the sister group of the branch holding animals and fungi, making these shapeless cells surprisingly close cousins of ours.
Most members crawl on blunt, finger-shaped pseudopods and have mitochondria with tube-like internal folds. Older textbooks ranked Amoebozoa as a phylum of protists or protozoa; the International Society of Protistologists treats it as an unranked supergroup within the eukaryotes. DNA evidence confirms all its members share one ancestor. Familiar names include Chaos, Entamoeba, Pelomyxa and Amoeba itself. They thrive in fresh and salt water, soil, moss and leaf litter, and a few live as parasites that can sicken humans.
Size varies astonishingly. Some cells measure only 10 to 20 micrometres, while Amoeba proteus reaches 800 micrometres, one reason teachers love it. Multinucleate Chaos and Pelomyxa can stretch several millimetres, and the slime mould Fuligo septica, nicknamed dog vomit, may carpet several square metres. Slime moulds achieve this by staying together after repeated divisions or by gathering into one mass.
A typical cell has a grainy core, the endoplasm, inside a clear outer layer, the ectoplasm. As it moves the core streams forward while the rim slides back, and many species take on a front and rear, sometimes acting as one big pseudopod. Most are naked, though Cochliopodium wears scales and the Arcellinida build rigid shells with a single opening, secreted in Arcella or cemented from gathered grains in Difflugia. All feed by engulfing particles into digestive vacuoles, and when food runs out most can form airborne cysts, called spores in slime moulds. Some Arcellinida host Chlorella algae inside them.
Flagella are rare, appearing in Archamoebae and in the paired-flagellum sex cells of many slime moulds; Archamoebae, living where oxygen is scarce, have lost their mitochondria. Thomas Cavalier-Smith grouped Amoebozoa with animals and fungi as unikonts, assuming a one-flagellum ancestor, but that assumption now looks wrong. Adl and colleagues proposed the name Amorphea in 2012, and newer work nests it inside a larger lineage called Opimoda.
Source: Amoebozoa
