''Paramoebidium'' is a genus of unicellular, symbiotic
eukaryotes that inhabit the digestive tract of immature freshwater
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
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 spec ...
larvae,
mayfly and
stonefly 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 Mesomycetozoea (or DRIP clade, or Ichthyosporea) 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 in ...
(= 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 The name is obsolete, having not been validly published.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 plac ...
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 (plural: 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. Many of these organisms were ...
) 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