Ramicristates

The Ramicristates are a diverse group of amoeboid protists that are characterized by the presence of branching tubular cristae? within the mitochondria. The vast majority of forms with lobose? and filose? pseudopods belong here.

The best-known member is Amoeba itself, found on decaying vegetation in freshwater streams and ponds. A number of lobose pseudopods extend from the front of the creature, fusing around food to trap it in internal vacuoles and spreading out to pull the creature along the substrate?. The outer layer of cytoplasm, the ectoplasm?, streams back from the pseudopods so acts like a tank-tread. A single contractile vacuole expels water to maintain the [osmotic balance]?.

A number of amoebae have protective shells. These may be formed by collecting and cementing together particles of sand, as in Difflugia?, it may be secreted, as in Arcella?, or it may be formed out of individually manufactured plates, as in Euglypha?.

Three types of slime molds also belong this group:

• The Myxomycetes?, true slime molds, which form a multinucleate plasmodium and are unusual in having a flagellate stage;
• The Dictyosteliida? and Protostelida?, both of which are cellular slime molds.