ambulacral

The term **ambulacral** refers to structures found in certain invertebrate animals, particularly echinoderms such as starfish, sea urchins, and sea cucumbers. These organisms possess an internal water vascular system that facilitates movement, feeding, and gas exchange through specialized tube feet. The term derives from the Latin *ambulare*, meaning "to walk," reflecting the role of these structures in locomotion.

In echinoderms, the ambulacral system is a hydraulic network that extends from a central ring canal. This system includes radial canals branching out to each arm or tube foot, which are connected to the madreporite—a sieve-like structure that links the water vascular system to the external environment. The tube feet, which are part of the ambulacral system, are used for gripping surfaces, locomotion, and capturing prey.

The ambulacral grooves, visible on the aboral (upper) surface of many echinoderms, mark the pathways of the water vascular system. These grooves are lined with ciliated epithelium and often contain sensory cells that detect environmental stimuli. The system relies on the movement of water driven by the contraction of myoepithelial cells, which pump water into the canals and extend the tube feet.

While the ambulacral system is most prominent in echinoderms, it also plays a role in some other invertebrates, such as certain types of sea slugs. In these organisms, it may assist in locomotion or feeding mechanisms. The structure and function of the ambulacral system highlight the evolutionary adaptations that enable these marine animals to thrive in diverse habitats.