''Opalina'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of parasitic

heterokont Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which a ...

s found in the

intestines The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

frog A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...

s and

toad Toad is a common name for certain frogs, especially of the family Bufonidae, that are characterized by dry, leathery skin, short legs, and large bumps covering the parotoid glands. A distinction between frogs and toads is not made in scient ...

s. They lack mouths and

contractile vacuole A contractile vacuole (CV) is a sub-cellular structure (organelle) involved in osmoregulation. It is found predominantly in protists and in unicellular algae. It was previously known as pulsatile or pulsating vacuole. Overview The contractile v ...

s, they are covered with nearly equal flagelliform cilia, and they have numerous nuclei, all similar. All the species are obligate endosymbionts, most likely commensal rather than parasitic, in cold-blooded

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

s. Its body is leaflike in shape. They lack

cytostome A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuol ...

s. They are saprozoic, consuming dead matter, which suggests their commensal role. They propagate by means of plasmotomy. The body is flattened, leaf-like and oval in outline and covered by thin pellicle. Nutrition is by pinocytosis. There are several small, spherical and similar sized nuclei present in the endoplasm. The nuclei are evenly distributed. The animal reproduces by longitudinal and transverse binary fission, or by plasmotomy in which the cell division is repeated again and again without division of nuclei. The daughter cells encysted and pass out in the faecal matter of the host. An example of a species is ''Opalina ranarum''.

References

Placidozoa Heterokont genera {{Heterokont-stub