Amorphea

Amorphea is a major supergroup of eukaryotes that includes Amoebozoa and Opisthokonta. The name reflects the variable (amorphous) morphology of many of its members. It is a relatively recent grouping based on molecular phylogenetic analyses, particularly those using ribosomal RNA and protein sequences. Prior to the widespread use of molecular phylogenetics, many of the organisms now classified within Amorphea were placed in different, often polyphyletic, groups.

The key defining characteristic, albeit not universally present, is the tendency to form blunt or lobose pseudopods, if pseudopods are present at all. Unlike other groups that employ filose (thin and branching) pseudopods, Amorphea members often use broader, more lobe-like extensions of the cell for movement and feeding. However, it's important to note that this characteristic is not universal, as some Amorphea lineages lack pseudopods entirely, or have modified pseudopods that are less readily classified as lobose.

The two primary groups within Amorphea are:

• Amoebozoa: This group includes many of the classic amoebae, characterized by their amorphous shape and use of lobose pseudopods for movement. Examples include Amoeba proteus, slime molds, and Entamoebida (parasitic amoebae).

• Opisthokonta: This group is characterized by cells possessing a single posterior flagellum at some point in their life cycle. Opisthokonta includes fungi, animals (Metazoa), and several groups of single-celled protists like choanoflagellates.

The close relationship between Amoebozoa and Opisthokonta, as demonstrated by molecular phylogenies, has revolutionized our understanding of eukaryotic evolution. It suggests a shared ancestry and common evolutionary trajectory for these diverse groups. While the morphological features can be variable, the genetic evidence strongly supports the monophyly of Amorphea.