Colpodella

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Colpodella: a tiny, free-living predator among alveolates

Colpodella is a small genus of single-celled organisms in the group Alveolata. They are free-living predators, not parasites, and feed on other protists. Most species are under 20 micrometers long and have two front-facing flagella.

Life cycle and feeding
- They have two main life stages: a motile flagellated form (trophozoite) and cysts, which are the reproductive stage.
- When feeding, Colpodella attach their front end to prey and suck out the prey’s cytoplasm into a large food vacuole. This feeding method is called myzocytosis.
- After feeding, they lose their flagella, become spherical, form a cyst, and divide to reproduce.

Structure and evolution
- They have a three-layer pellicle and alveolar membranes, with vesicular mitochondrial cristae.
- They possess a simple, open conoid (pseudoconoid) at the front, unlike the closed conoids of true Apicomplexa.
- During feeding, a ring of microtubules forms around the attachment area.
- Colpodella is thought to be closely related to Apicomplexa and may represent free-living ancestors of that group.

Species and classification
- The genus includes about five described species, with a couple more possible.
- Some species were once placed in Spiromonas; the type species is Colpodella pugnax.

Human health
- They are not usually human pathogens, though there has been at least one report of erythrocyte infection in a person with immune deficiency.

Related genera
- Acrocoelus is another genus in the same family.