''Paramoebidium'' is a genus of unicellular, symbiotic
eukaryote
The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
s that inhabit the digestive tract of immature freshwater
arthropod
Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...
hosts (e.g.
black fly
A black fly or blackfly (sometimes called a buffalo gnat, turkey gnat, or white socks) is any member of the family Simuliidae of the Culicomorpha infraorder. It is related to the Ceratopogonidae, Chironomidae, and Thaumaleidae. Over 2,200 s ...
larvae,
mayfly
Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the orde ...
and
stonefly
Plecoptera is an order of insects commonly known as stoneflies. Some 3,500 species are described worldwide, with new species still being discovered. Stoneflies are found worldwide, except Antarctica. Stoneflies are believed to be one of the most ...
nymphs).
[Lichtwardt, R.W., M.J. Cafaro, M.M. White. 2001. The Trichomycetes: Fungal Associates of Arthropods Revised Edition. Published online http://www.nhm.ku.edu/%7Efungi/Monograph/Text/Mono.htm ] ''Paramoebidium'' is classified in the
opisthokont
The opisthokonts () are a broad group of eukaryotes, including both the animal and fungus kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and ...
class
Mesomycetozoea
The Ichthyosporea (or DRIP clade, or Mesomycetozoea) are a small group of Opisthokonta in Eukaryota (formerly protists), mostly parasites of fish and other animals.
Significance
They are not particularly distinctive morphologically, appearing i ...
(= Ichthyosporea), and is the sole genus in the family Paramoebidiidae. Prior to 2005, ''Paramoebidium'' species were tentatively placed with the fungal group
Trichomycetes
Trichomycetes refers to a group of fungi in the division Zygomycota that grow in the guts of arthropods living in aquatic habitats. The name is obsolete, having not been validly published. Species formerly placed in the Trichomycetes are now place ...
due to their habitation of arthropod guts, host overlap between various ''Paramoebidium'' and fungal trichomycete taxa, and similar vegetative growth form.
[Moss, 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.]
Etymology
The prefix "para-", roughly meaning "similar to", refers to the assumed relatedness of ''Paramoebidium'' to the genus ''
Amoebidium
''Amoebidium'' is a genus of unicellular, symbiotic eukaryotes in the Opisthokont group Mesomycetozoea, family Amoebidiidae.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. ...
''.
Members of both genera may produce motile, amoeba-like dispersal cells during their life cycle.
The similarity of life cycle, morphology, and ecology lead to the hypothesis that ''Amoebidium'' and ''Paramoebidium'' were minimally closely related, and probably
sister taxa
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
.
Description
''Paramoebidium'' species are unicellular. The vegetative cells (=
thalli
Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...
) 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.
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