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

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

Filter Feeding in Polychetes The fourth example occurs in Sabella  These animal is large worm  It builds tube and projects from the surface of the mud by its head and the branchial crown  It is a suspension feeder, extracting its food from water currents by coordinated cilia that cover the crown.

Filter Feeding in Polychetes The structure of Branchial Crown:  It consists of a large number of cephalic tentacles or filaments being stiff and pinnate and arranged in two groups of about 30  Each group is united towards its base into a lateral lobe.  The two lobes are joined together dorsally and extend back on the ventral surface.  The branchial crown forms a wide funnel and its base is the mouth of the animal

Filter Feeding in Polychetes Operation of the Branchial Crown Its operation in feeding depends upon:  Two rows of outgrowths of pinnules  A pinnule in one row makes an angle more than 90° with the corresponding pinnule in the other row.  The pinnules at the distal end of a filament are separated from the ones on the next adjacent filament.  Towards the lower part of the branchial funnel, they are brought closer together and finally interlocked.  Means, they forms a filtering system upon which food particles can be trapped.

 Structure of the pinnule:  The outer surfaces of the pinnules bear cilia  There are three types of cilia on each pinnule (abfrontal, latero- fronta and frontal) o The abfrontal cilia beat strongly towards the tip of each pinnule and draw water into the funnel. o The latero-frontal cilia beat inwards at right angle to the beat of the abfrontal ones o The result of beating of the two kinds of cilia is enterance of food particles into the funnel with the stream of water that run onto a groove which is formed along the inner edge of each pinnule. o The frontal cilia covering the groove beat towards the base of the pinnule in the opposite direction to the beat of the abfrontal ones o The frontal cilia drive the food particles to the bases of the pinnules Filter Feeding in Polychetes

 Structure of the base of filament:  Towards the base of each filament the two rows of pinnules pass into two continuous folds (basal folds)  These folds are ciliated on both their outer and inner faces o The cilia mostly beat upwards towards the free edge of the folds, but on their inner surfaces the folds bear three ciliary tracts in which the beat is downwards. o This downward beat is directed towards the mouth which is bordered by a dorsal and two lateral lips  The lips are formed in part from the bases of a pair of long palps and in a part of the branchial crown. o The lips are ciliated and they bear three ciliary tracts that correspond with the three tracts of the folds.

Filter Feeding in Polychetes These various structures constitute part of th e sorting mechanism  Sorting mechanism means the capacity of branchial crown to differentiate between particles of various sizes (i.e. large, medium and small particles)  Pinnules play some part in this mechanism.  Large particles fall from above with the food stream cannot enter the longitudinal grooves of the filaments since these are protected by the overarching of the expanded bases of the pinnules.  Folds play another part in this mechanism.  Each pair of fold enclose a basal groove and the inner surfaces are so close together that large particles cannot enter between them and they are moved away from the mouth towards the edges of the lips. They are removed from the animal through the action of rejection current that create by the cilia of palps and lips.  The smallest particles can pass between the inner surfaces of the folds into the basal groove and they are then carried towards the mouth.  The medium-sized ones can enter between the inner surface of the folds and transport into the two expansions of the lateral lips called the ventral sacs and also cannot enter the mouth. They are mixed with mucus for the building of the mud tube.

In the animals feed by filter feeding mechanism, the digestion takes place by extracellular. The gut shows considerable regional specialization for this type of digestion The cells of intestinal epithelium has the capacity for phagocytosis Fore-stomach and fore- intestine secrete enzymes Absorption takes place in the intestine. Digestion in Polychetes