Examples
For example, flagellate protozoans of the genus Euglena move towards a light source. Here the directional stimulus is light, and the orientation movement is towards the light. This reaction or behaviour is a positive one to light and specifically termed "positive phototaxis", since phototaxis is a response to a light stimulus, and the organism is moving towards the stimulus. If the organism moves away from the stimulus, then the taxis is negative. Many types of taxis have been identified and named using prefixes to specify the stimulus that elicits the response. These include aerotaxis (stimulation by oxygen) anemotaxis (wind), barotaxis (pressure), chemotaxis (chemicals), galvanotaxis (electrical current), gravitaxis (gravity), hydrotaxis (moisture), magnetotaxis (magnetic field), phototaxis (light), rheotaxis (fluid flow), thermotaxis (temperature changes) and thigmotaxis (physical contact).
Depending on the type of sensory organs present, taxes can be classified as klinotaxes, where an organism continuously samples the environment to determine the direction of a stimulus, tropotaxes, where bilateral sense organs are used to determine the stimulus direction, and telotaxes, which are similar to tropotaxes but where a single organ suffices to establish the orientation movement.
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