Structure and function

The anatomy of abalone is complicated. The effects of torsion and other developmental constraints, the dramatic flattening and open spiral of the shell, and the central location of the highly enlarged right columellar muscle impact the placement and morphology of the major organs as well as the circulatory and nervous systems. The details of how many of the major organs function are still being investigated. The anterior head has a pair of sensory tentacles and stalked eyes. The ventral mouth leads to a buccal region with an elaborate odontophoral apparatus to take in food. The large dorsal mantle cavity is filled by two bipectinate gills, or ctenidia. All other exchanges with the environment, including gas exchange, collection of sensory information about the incurrent water, elimination of wastes, and the release of gametes, occur in the mantle cavity via the movement of water through incurrent and excurrent openings, or tremata, in the shell. The enlarged foot consists of complex networks of collagen-wrapped muscle fibers. The mantle lines the mantle cavity, covers the organs, and secretes the layers of the shell. The digestive system has complex regional specialization and loops posteriorly and anteriorly within the body. The heart consists of two auricles and a ventricle. The heart receives hemolymph from the gills, and pumps it via arteries through unlined capillary-sized spaces in the organs to veins that carry most of it to the gills for gas exchange. The coelom of adults is restricted to the pericardial and renal cavities. The left and right kidneys are distinctly different in structure and function. Sexes are separate. The large gonad is divided into chambers by trabeculae and gametes move to the right kidney, where they are released into the mantle cavity. The streptoneurous nervous system consists of a series of ganglia from which extend nerves to all the tissues of the body. Specialized sensory structures include the chemosensory osphradium located in the mantle cavity; sensory bursicles on the ctenidial leaflets; cephalic, epipodial, and mantle tentacles; statocysts; and eyes.