atriopores

Atriopores are external openings that communicate with the atrial cavity in cephalochordates, most notably in amphioxus ( Branchiostoma ). They serve as the exit point for water that has passed through the pharyngeal slits into the atrial chamber, completing the water flow essential for feeding and respiration in these animals.

In the amphioxus water pathway, sea water enters through the mouth, moves through the pharynx and its slits, collects in the atrial (atrium) cavity, and then flows out to the exterior via the atriopore. The atrial cavity thereby functions as a reservoir that helps separate food particles from the water before digestion, while the expelled water aids in circulation and respiratory exchange.

Anatomically, an atriopore is a small external opening connected to the atrium. The number and precise position of atriopores can vary among species, and in some taxa there may be a single atriopore. The term is primarily used in descriptions of cephalochordate anatomy; it is less common in vertebrate anatomy where analogous structures are described differently.

Etymology derives from Latin atrium, meaning inner chamber, and pore, indicating an opening. While atriopores are characteristic of the cephalochordate water-transport system, the concept illustrates how ancient chordates managed internal water flow for feeding and respiration before the evolution of more complex circulatory and respiratory organs. See also amphioxus, cephalochordates, pharyngeal slits.