2. Filter Feeding  In Polychetes  In Molluscs  In Deuterosmia  In Crustaceans Respiration  Physical factors  Pigments  Gills and Lophophores in Polychetes  Gills and Lungs in Molluscs  Gills and Trachea in Arthropods Syllabus

4. Filter Feeding Filter Feeding Remember This type is found only in aquatic animals It is disappeared from the terrestrial animals due to the lower density of air It is occurred in small aquatic animals It takes place through special organs

5. Digestion in Molluscs The ingestion of small particles probably determined the retention of the:  Intracellular method of digestion.  The alimentary system adapted for microphagy.  The stomach is a characteristic part in the alimentary tract.  This type of digestion requires a large area of phagocytic epithelium  The food must be delayed in its passage through the alimentary tract and distributed over the epithelium.

6. Digestion in Molluscs The structure of the stomach In bivalves:  A A long crystalline style and flexible rod projects into the lumen of the stomach. TThis rod is composed of layers of mucoprotein TThis rod is secreted by a style sac which is an extension of the stomach. TThe style sac contains cilia causing the style to rotate, and to drive it forwards into the stomach. TThe free end of the style is worn away by friction against the gastric shield, which is a thickening of the cuticular lining of the stomach wall. TThis causes dissolving of the style substance containing a digestive amylase TThis substance is added to the contents of the gastric lumen.

7. The sorting mechanism in the stomach of bivalves:  Food particles enter the stomach with strands of mucus, are mixed with the digestive secretion by the rotation of the style, so that the extracellular digestion of carbohydrate is initiated.  Particles of food are continually broken off and sorted by the stomach wall.  The stomach wall is lined with ciliated ridges and grooves that have an action similar to that of the labial palps.  The larger and heavier particles enter the deeper grooves and are transported by cilia into the intestine and the effect of more alkaline pH forming them into faecal pellets that extruded through the anus.

8.  The fine particles are borne over the cilia on the ridges of the stomach wall towards the opening of the digestive diverticula or glands.  There are two diverticula, each consisting of a highly branched system of blined tubules opening into the stomach by ciliated duct. The epithelium of these tubules are also ciliated and is composed of highly vacuolated cells. These cells are highly phagocytic, capable of ingesting fine particles into food vacuoles and the digestion is completed inside the vacuoles.  The intracellular digestion takes place. Filter Feeding in Molluscs