Protosteloid amoebae (protosteliida, protosporangiida, cavosteliida, schizoplasmodiida, fractoviteliida, and sporocarpic members of vannellida, centramoebida, and pellitida)

Abstract

Protosteloid amoebozoans, formerly called protostelids, are a non-monophyletic assemblage of Amoebozoa where, at one point in their development, an amoeba rounds up on the surface of a substrate and develops into a subaerial fruiting body, or sporocarp. The sporocarp consists of a noncellular, microscopic stalk bearing one to a few terminal spores. Amoeboid states of protosteloid amoebae vary considerably in morphology, and many species have life cycles that include both amoeboflagellates, a cell type that can reversibly transform from amoeba to flagellate, and obligate amoebae, a cell type that exists only as an amoeba. Protosteloid development was first recognized in Protostelium mycophaga and has been observed in perhaps 100 species, roughly 40 of which are formally named. Protosteloid amoebae are predators of decomposer bacteria and fungi in terrestrial ecosystems. They are global in distribution. Most are quite easy to isolate and to bring into culture, thus facilitating developmental studies. Sporocarpy, as a mode of development, is found in protosteloid amoebae and in myxogastrids; it is exclusive to Amoebozoa. This raises the question whether it is a homologous process or whether it has arisen independently multiple times within Amoebozoa. If the former proves to be the case, it would suggest that the last common ancestor of Amoebozoa must have had a sporocarp in its life cycle.