Paramoebidium is a genus of unicellular, symbiotic eukaryotes that inhabit the digestive tract of immature freshwater arthropod hosts (e.g. black fly larvae, mayfly and stonefly nymphs).[2]Paramoebidium is classified in the opisthokont class Mesomycetozoea[3] (= Ichthyosporea[4]), and is the sole genus in the family Paramoebidiidae.[5] Prior to 2005,[6]Paramoebidium species were tentatively placed with the fungal group Trichomycetes due to their habitation of arthropod guts, host overlap between various Paramoebidium and fungal trichomycete taxa, and similar vegetative growth form.[7]
The prefix "para-", roughly meaning "similar to", refers to the assumed relatedness of Paramoebidium to the genus Amoebidium.[1] Members of both genera may produce motile, amoeba-like dispersal cells during their life cycle.[7] The similarity of life cycle, morphology, and ecology lead to the hypothesis that Amoebidium and Paramoebidium were minimally closely related, and probably sister taxa.[2]
Paramoebidium species are unicellular. The vegetative cells (= thalli) have an elongate, hair-like growth form with a secreted, glue-like holdfast at the base that attaches them to the host digestive tract lining.[2] Sexual reproduction is unknown. During asexual reproduction, the entire content of the cell is partitioned into many motile amoeboid cells. The cell wall breaks down and the amoeboid cells are released. These amoeboid cells are termed "dispersal amoebae" because they crawl for a short time before encysting. The cyst expands and forms several spores (called cystospores) that are released when mature.[1]
There are currently 17 validly described species of Paramoebidium.[2] Several other species were described but are considered invalid due to a lack of descriptive detail and/or illustrations.[2][8] Species have been described based on the morphological features of the thalli, cysts, and cystospores. Host type is also reported for species, but it is unclear how host specific different Paramoebidum species may be.[2] Thallus shapes range from straight, short, and fat to long and sigmoidal, to branched or coiled. For example, P. curvum[9] have short, coiled, thick thalli and are found in black fly larvae (Simuliidae), whereas P. hamatum[10] have relatively long thalli that are consistently curved near the base giving them a "candy cane" appearance and are associated mainly with mayfly nymphs (Ameletidae and Baetidae) but also midge larvae. However, while Paramoebidium species are relatively common among trichomycete collections,[11][2] description of new species is problematic due to the amount of intra- and interspecific variability of the morphological characters.[12] Furthermore, no species have been obtained in axenic culture, so observations are limited to the individuals present at the time of host dissections and some stages of the life cycle (e.g. dispersal amoebae) may not be present in the collection.
^ abcLéger, L., and Duboscq, O. 1929. L'évolution des Paramoebidium, nouveau genre d'Eccrinides, parasite des larves aquatiques d'Insectes. Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences Paris189: 75-77.
^Cavalier-Smith, T. 1998. Neomonada and the origin of animals and fungi. In: Coombs GH, Vickerman K, Sleigh MA, Warren A (ed.) Evolutionary relationships among protozoa. Kluwer, London, pp. 375-407.
^Reynolds, N.K., M.E. Smith, E.D. Tretter, J. Gause, D. Heeney, M.J. Cafaro, J.F. Smith, S.J. Novak, W.A. Bourland, M.M. White. 2017. Resolving relationships at the animal-fungal divergence: A molecular phylogenetic study of the protist trichomycetes (Ichthyosporea, Eccrinida). Molecular Phylogenetics and Evolution in press, available online 20Feb.2017. https://dx.doi.org/10.1016/j.ympev.2017.02.007
^Cafaro, M. 2005. Eccrinales (Trichomycetes) are not fungi, but a clade of protists at the early divergence of animals and fungi. Molecular Phylogenetics and Evolution 35: 21-34.
^ abMoss, S.T., 1979. Commensalism of Trichomycetes. In L. R. Batra, ed. Insect-Fungus Symbiosis Nutrition, Mutualism, and Commensalism. Montclair: Allanheld, Osmun & Co. Publishers, Inc., pp. 175–227.
^Duboscq, O., Léger, L., and Tuzet, O. 1948. Contribution à la connaissance des Eccrinides: les Trichomycètes. Archives de Zoologie Expérimentale et Générale 86: 29-144.
^Dang, S., and Lichtwardt, R. W. 1979. Fine structure of Paramoebidium (Trichomycetes) and a new species with viruslike particles. American Journal of Botany66: 1093-1104.
^Bench, M.E., M.M. White. 2012. New species and first records of trichomycetes from immature aquatic insects in Idaho. Mycologia 104(1): 295-312.
^Lichtwardt, R. W., and Williams, M. C. 1992a. Two new Australasian species of Amoebidiales associated with aquatic insect larvae, and comments on their biogeography. Mycologia84: 376-383.
^Valle, L.G. 2014. New species of Paramoebidium (trichomycetes, Mesomycetozoea) from the Mediterranean, with comments about the amoeboid cells in Amoebidiales. Mycologia 106(3): 481-490.
