A form of taxis characterized by the directional movement of an organism in response to gravity
Taxis is a behavioral response of a cell or an organism to an external stimulus. The movement is characteristically directional. The movement may be positive or negative. A positive taxis is one in which the organism or a cell moves towards the source of stimulation (attraction). A negative taxis is when the organism or a cell moves away from the source of stimulation (repulsion).
Gravitaxis is one of the many forms of taxis. It is characterized by the movement of an organism in response to gravitational forces. An example of gravitaxis is the response of planktonic larvae of Lithodes aequispinus (king crab) to gravity. They show both positive and negative gravitaxes in a way that they move either upward (positive) or downward (negative).1
Gravitaxis is different from gravitropism in a way that the latter is more about the growth response of an organism to gravity.
Word origin: gravi- (relating to gravity) + taxis
1 Adams, C. F. & Paul, A. J. (1999). "Phototaxis and geotaxis of light-adapted zoeae of the golden king crab Lithodes aequispinus (Anomura: Lithodidae) in the laboratory". Journal of Crustacean Biology 19 (1): 106–110.