STUDIES ON FUNCTIONAL MORPHOLOGY IN THE DIGESTIVE SYSTEM OF OREASTER RETICULATUS (L.) (ASTEROIDEA).

This paper presents, with illustrations, a description of the digestive system of Oreaster reticulatus, a species for which such anatomical details have hitherto been unavailable. Special features of the digestive system include a large, highly eversible cardiac stomach with a particularly well-developed system of securing and retracting fibers; a highly specialized pyloric stomach giving rise to paired pyloric caeca, each of which is associated with an unusually elaborate Tiedemann's pouch featuring a series of secondary pouches branching off along its length; and a set of very voluminous intestinal caeca. By comparison with other asteroids for which anatomical details and feeding biology are known (especially Patiria miniata and Porania pulvillus), it is suggested that O. reticulatus is equipped for a variety of modes of feeding. The cardiac stomach is well adapted for the digestion of large pieces of food outside the body; it may also function as a flagellary-mucous particle-collector, as the similar organ of Patiria is thought to do. The specializations of the upper part of the digestive system are closely similar to corresponding organs in the known particle-feeding species Porania pulvillus, and it seems probable that Oreaster may use its Tiedemann's pouches and intestinal caeca to bring particle-laden water into the digestive system in a manner similar to that described for Porania. Such direct observations as are available on the feeding behavior of O. reticulatus tend to confirm the conclusions inferred on indirect, anatomical grounds.