- Colorless, heterotrophic protists with multiple flagella found as endosymbionts (commensals) in the hindgut of cold-blooded vertebrates (e.g., frogs, toads and fish).
- The trophic stage is apparently diploid.
- When swimming the flagella beat in a metachronal fashion.
- Individual cells contain multiple nuclei that are typically conspicuous.
- Cells are covered by a furrowed or pleated (folded) pellicle.
- A falx is present at the anterior ends of cells from which flagella (and their basal bodies or kinetids) on the somatic cell body arise following cell division. During cell division the falx is bisected by a line parallel to, or oblique to, the anterior-posterior axis of the cell.
- Endosymbiotic opalinid trophic and reproductive stages are apparently microaerophilic.
- The organisms lack a cytostome (mouth) and obtain nutrition by pinocytosis.
- Asexual reproduction is via binary fission (more-or-less longitudinal) and the nuclear envelope remains intact during mitosis.
- Motile, uninucleate, haploid anisogametes (gametes of different sizes) are produced via meiosis that resemble the mother cell in miniature. Anisogametes fuse giving rise to diploid cells.
- Small cysts with reduced numbers of nuclei are passed out of the host’s body in fecal material.
Four opalinid genera are presently recognized: Cepedea, Opalina, Protoopalina, Zelleriella. These genera are separated from one another based upon the shape of the organism in cross-section and the number of nuclei per cell. According to Corliss (1990) over 400 opalinid species have been described but the actual number of species is likely to be much lower. Species placed in Cepedea and Opalina possess numerous nuclei per cell whereas Protoopalina and Zelleriella are binucleate.
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- First online 28 April 2010
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