Why do some animals remain sessile rather than move to find food?

Some animals remain sessile—permanently attached to a surface rather than moving about—because the energy and nutrients required to maintain active locomotory capabilities can be more efficiently diverted into growth or the production of offspring.1

By adopting a sedentary strategy, these animals rely on water or air currents, or the movement of potential prey, to bring food within their reach. This lifestyle often leads to the development of strong physical defenses, such as shells or toxins, which may be incompatible with the body structures required for effective locomotion. Because food may arrive from any direction, many sessile animals have evolved radial symmetry to better capture resources.1

While sessile animals do not actively hunt, they are not entirely passive; they may actively choose their attachment sites to maximize feeding efficiency, and at least one stage of their life cycle is typically capable of movement to ensure dispersal.1