Amoebidiidae
| Amoebidiidae | |
|---|---|
| Scientific classification | |
| Domain: | Eukaryota |
| (unranked): | Opisthokonta |
| (unranked): | Holozoa |
| Class: | Mesomycetozoea |
| Order: | Ichthyophonida |
| Family: |
Amoebidiidae Lichtenstein |
| Genera | |
Amoebidiidae is a family of single-celled eukaryotes, previously thought to be zygomycete fungi belonging to the class Trichomycetes, but molecular phylogenetic analyses place the family with the opisthokont group Mesomycetozoea (= Ichthyosporea). The family was originally called Amoebidiaceae, and considered the sole family of the fungal order Amoebidiales that included two genera: Amoebidium and Paramoebidium. However, Amoebidiidae is now monogeneric as it was recently emended to include only Amoebidium (and Paramoebidium is now the sole genus of the family Paramoebidiidae). Species of Amoebidium are considered obligate symbionts of freshwater-dwelling arthropod hosts such as midge larvae and water fleas (Daphnia). However, because Amoebidium species attach to the exoskeleton (exterior) of the host and grow in axenic culture, at least some species may be facultative symbionts.
The "amoeb-" prefix refers to the amoeba-like dispersal cells that are produced during the life cycle of Amoebidium.
As the family is monogeneric, the description follows that of the genus, Amoebidium. 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).
The classification of Amoebidium and Paramoebidium with the fungal trichomycetes was early considered tenuous due to the production of amoeboid dispersal cells, a feature not seen among Fungi. Later studies found no evidence of chitin in the cell wall of these species, further casting doubt on their relatedness to Fungi. However, their overall morphology (i.e. hair-like growth form with a basal holdfast), production of spores, and residence in the digestive tract of arthropods were considered strong enough characters to include them with the fungal trichomycetes until additional evidence could resolve their placement.
...
Wikipedia