Digestive system

The mouth, present on the underside or oral surface of the starfish, is the entrance to the digestive system (figure 2) (Ruppert et al. 2004). It is located within a peristomial membrane and possesses a short esophagus leading into the two main sections of the stomach, the larger oral cardiac stomach and the small aboral pyloric stomach (Ruppert et al. 2004). The pyloric stomach possesses a pair of pyloric cecum in each arm of the animal, which are line by ducts (Ruppert et al. 2004).These ducts have cilia that create incoming and outgoing water flows (Ruppert et al. 2004). The pyloric ceca are the primary sites of digestion and absorption (Ruppert et al. 2004). The pyloric stomachis joined to the rectum via a tubular, short intestine (Ruppert et al. 2004). The rectum functions as a site of waste formation of indigestible matter and opens up to a tiny anus, where faeces are released (Ruppert et al. 2004). The rectum also possesses numerous recal ceca, which are the site of some absorption that does not occur in the pyloric ceca (Ruppert et al.2004). The cardiac stomach is important in ingestion of food. 


the anus and mouth of N.cumingi

Feeding

Asteroids are able to feed in two ways; extraorally and intraorally (Ruppert et al. 2004). Extraoral ingestion occurs through evertion of the cardiac stomach through the mouth (Ruppert et al. 2004). This evertion is possible through the use of body wall muscles, which contract causing a buildup of coelomic pressure resulting in the expulsion of the stomach (Ruppert et al. 2004). To ensure the stomach remains attached to the individual it is anchored by gastric ligaments (Ruppert et al. 2004). The everted stomach drapes over the prey item, secretes digestive enzymes produced by the stomach and pyloric ceca, and then proceeds to consume the prey (Ruppert et al. 2004). Following consumption of the prey item the stomach is retracted back into the body of the organism with the contraction of the stomach muscles (Ruppert et al. 2004). This method is primarily used in ‘advanced’ asteroids (Tokeshi 1991). Although the exact method of feeding of N.cumingi is unknown, the order Valvatida,  to which they belong, is an evolutionarily advanced group which employ the technique of extraoral feeding (Tokeshi 1991). It can therefore be inferred that N.cumingi are likely to employ this technique of feeding. The more primitive asteroids however utilise intraoral feeding, where the prey is consumed whole and digested internally (Tokeshi 1991).