Protozoa are a diverse group of unicellular eukaryotic organisms, many of which are motile. Originally, protozoa had been defined as unicellular protists with animal-like behavior, e.g., movement. Protozoa were regarded as the partner group of protists to protophyta, which have plant-like behaviour, e.g., photosynthesis.
Vorticella is a genus of protozoa, with over 16 known species. They are stalked, inverted bell-shaped ciliates, placed among the peritrichs. Each cell has a separate stalk anchored onto the substrate, which contains a contractile fibril called a myoneme. When stimulated, this shortens, causing the stalk to coil like a spring. Vorticella species mainly live in freshwater ponds and streams—generally anywhere protists are plentiful.
Reproduction is by budding, where the cell undergoes longitudinal fission and only one daughter keeps the stalk. The free daughter becomes a telotroch, which swims until it finds suitable substrate to fix and develop its own stalk. They reproduce by fission, which is also known as cell division. They are also capable of reproducing by conjugation, a form of sexual reproduction where two individuals attach at the oral groove and exchange DNA.
Other genera, such as Carchesium, resemble Vorticella, but are branched or colonial.
Vorticella species sometimes stay in clusters or groups considered as colonies, but they are not true colonies because each cell has its own individual stalk. This allows it to detach from the cluster at any time, usually by reverting to a telotroch when environmental conditions are unfavorable.
An epibiont is an organism that lives on the surface of another living organism. An epibiont is usually considered harmless to the host; in this sense, the relationship between the two organisms can be considered neutralistic or commensalistic. Typical epibionts are barnacles, remoras, and algae, all of which live on many larger marine organisms, such as whales, sharks, sea turtles, and mangroves. The host of the epibiont is typically referred to as the basibiont.