Bigyra is a diverse group of
heterotrophic, mainly
phagotrophic
stramenopiles that lack
cell walls. It contains three well-known important groups with widely different ecological functions and morphologies:
labyrinthulomycetes,
opalines and
bicosoecids.
Labyrinthulomycetes is a group of
protists that absorb nutrients in an
osmotrophic or
phagotrophic manner. They can behave either as free-living
amoebae or as
mycelium-like networks of
cytoplasmic threads. Some of them are
saprotrophic decomposers of the
detrital food web; as such, they play a role in making organic matter more accessible to other
organisms. Others are
parasitic, and others are predators of
bacteria. They are
cosmopolitan,
ubiquitous in
marine,
freshwater and
estuarine environments. They live in association with
algae, marine
plants and
detritus.
Opalinata is a diverse assemblage of modified
parasitic protists known as 'opalines'. They inhabit the
intestines of various
animals, primarily
amphibians. They are found on every
continent. Among them, the
opalinids are highly unusual protists: their large cells have numerous flagella and from two to hundreds of
nuclei. Their
cell surface is delicately folded, giving it an
iridescent appearance (hence their name, a reference to the iridescent
opal). Another important group of opalines is
Blastocystis, a prevalent parasite of humans and other animals.
Bicosoecida is a small group that contains free-living
marine and
freshwater nanoflagellates that feed on
bacteria. They are present in every ecosystem, including extreme environments such as the deep sea or salt flats. They play a crucial role in the
microbial food web by composing the link between bacteria and higher
trophic levels. They are also important in biogeochemical cycles by remineralizing the nutrients. Their classification has changed multiple times over the years, and is still an unresolved issue. ==Evolution and systematics==