Amoebidium

Amoebidium
Scientific classification
Domain:	Eukaryota
(unranked):	Opisthokonta
(unranked):	Holozoa
Class:	Mesomycetozoea
Order:	Ichthyophonida
Family:	Amoebidiidae
Genus:	Amoebidium Cienkowski

Amoebidium Cienkowski, 1861 is a genus of unicellular, symbiotic eukaryotes in the opisthoknont group Mesomycetozoaea, family Amoebidiidae.Amoebidium species attach to the exoskeleton of freshwater aquatic arthropods such as midge larvae and water fleas (Daphnia). The type species is Amoebidium parasiticum, which is also one of the only species to be cultured axenically.

Derived from the word "amoeba" to refer to the amoeba-like dispersal cells formed during some stages of the life cycle.

Amoebidium species are single-celled, cigar-shaped or tubular in vegetative growth form (= thallus), and attach to the exoskeleton of various freshwater arthropod hosts (Crustaecea or Insecta) by means of a secreted, glue-like basal holdfast. The thalli are coenocytic (i.e. lack divisions within the cell) and are unbranched. Sexual reproduction is unknown. Asexual reproduction may proceed along two different routes: 1) the entire content of the cell divides into elongated, uninucleate spores (known as sporangiospores or endospores) with the cell wall breaking apart to release the spores or 2) the entire content of the cell divides to produce teardrop-shaped, motile amoeboid cells that disperse for a short time, then encyst and produce spores from the cyst (called cystospores).

There are currently five species that have been named and are differentiated based on the size and shape of the thalli, spores, and dispersal amoebae. Amoebidium parasiticum is the most commonly encountered species in field collections, and appears to have a cosmopolitan distribution with collections from the Czech Republic, Denmark, England, France, Israel, Japan, the Philippines, Poland, Puerto Rico, Singapore, Spain, Tunisia, and the USA. It has also been found in association with a variety of hosts including copepods, amphipods, isopods, mayfly nymphs, and black fly and midge larvae. The other four species (A. appalachense,A. australiense,A. colluviei, and A. recticola) have been collected from limited geographic areas, but it is unclear whether these species truly have a limited distribution or if the observed distribution is an artifact of limited sampling. For example, A. recticola has not been reported in the literature since 1920 and was originally collected from Daphnia living in a reptile tank at the Paris Museum, France.

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