Papers from the Echinoderm Conference. 2. Etude structurelle et fonctionnelle du tube digestif d’Asterias rubens Linnaeus (Echinodermata: Asteroidea)
The digestive tract of A. rubens is composed of three morphologically and physiologically main regions: the floor of the cardiac stomach, the diverticula of the pyloric caeca and the rectal caeca. These regions are linked by transit zones (ciliary channels of the pouches and the upper part of the cardiac stomach, of the pyloric ducts, of the pyloric stomach and of the intestine).
During the meal the everted stomach - cardiac floor - is in intimate contact with the soft parts of the prey. The cardiac zymogen cells secrete their enzymes and extra-oral digestion occurs (extracellular digestion). Some particles of food are embedded in mucus and passed to the pyloric ducts by the ciliary channel of the cardiac stomach. At the same time the rectal current carries some small food particles directly into the rectal caeca where they are absorbed (intracellular digestion). The pyloric enzymes digest the food that has passed into the pyloric diverticula. The digestive products are then absorbed (extracullar and intracellular digestion).
The digestion by Asterias is virtually complete, little faecal matter being passed through the anus. Defecation is the result of the contraction of the rectal caeca wall, associated with the relaxing of the anal sphincter. The average duration of a meal is between five and six hours.