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Syllabus
 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
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
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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.
Filter Feeding in Polychetes
 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)
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The abfrontal cilia beat strongly towards the tip of each pinnule and draw
water into the funnel.
The latero-frontal cilia beat inwards at right angle to the beat of the
abfrontal ones
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.
The frontal cilia covering the groove beat towards the base of the pinnule
in the opposite direction to the beat of the abfrontal ones
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
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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.
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 the 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.
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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.
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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.
Digestion in Polychetes
• In the animals feed by filter
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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 foreintestine secrete enzymes
Absorption takes place in the
intestine.