Mode of nutrition and feeding in invertebrate.
Feeding habits of animals varies from one from of animals to another. Based on
nutritional mode of animal animals are group into:
Holozoic---Solid/semi solid foods are swallowed both obtained from plants and animals.
Eg spnges,arthopodes.
Holophytic---Sythesised own food. Eg euglena
Saprophytes—Absorbed food from the dead decaying materials. Eg Annelids
Coprozoic—obtain from dung and faecal matter eg beetle
Parasitic—obtained by ectoparasitic and endoparasitic mode.
Animals are also grouped into herbivorous, carnivorous and omnivorous.
Protozoa
Feeds on diatoms and phytoplanktons and bacteria. Holozoic in nutrition.
Ingest in various ways :
Circumvallation_cup formation
Circumfluance—amoeboic movement.
Import—filament sinks into cytoplasm
Digestion---digest within the vacuole
Absorption---by diffusion
Egestion --through opening like cytophage
--through contractile vacuole
Sponges
Holozoic in nutrition, feeds on minutes organismsand degenerating materials
Inner lining of spongocoel has layer of choanocytes and has “collar”
Collar of choanocyte allows only the water to let out and traps the food particles.
Water current bring the preys into the collar of chaonocytes which is then traped partially
digested in the collar cell itself.
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Later it is passed to ameboid cells in mesogleal layer for thoroughly digested.digested
food is stored in the amoeboid cells.
Thus digestion is intra cellular digestion brought about by two cells.
Coelenterata
Holozoic in nutrition, feeds on crustacean, insect larvae and smaller animals.
During feeding organism normally remain motionless tentacles trailing in water.
If prey is passed by the one of the nearest tentacle releases poison through the cells
(nematocyst) ‘expolsion”, chemical released would paralyze the animal.
Finally the tentacle wrapped around the prey and contracts to draw the prey close to the
mouth.
No. of tentacle involved in trapping prey depend on stimulus of prey or food.
Digestion begins once it enters the gastrovascular ( enteron)via mouth.
Distilled region of endodermal cells have more glands that secretes digestive juice, it
reduces the prey to smaller fragment.
Digestible food is the taken into vacuole by the pseudopodial activity of endodermal
cells.The digestion is began in enteron leading extracellular digestion like most higher
group animals and complete it digestion in endodermal cell thus intracellular digestion
like protozoa.
Undigested are returned to cell surface for exocytosis
Platyhelminthes
Parasatic mode of life.
Completely dependent to the digested food of host
Digestive of this animal are poorly developed like planaria, well developed in liver fluke
(feeds on host muscles thus need to digestive system) and completely absent in most of
the animals like tapeworm
Absorption of food by simple diffusion through body surface.
Nemahelminthes
Feeds on digested food of its host the food is suck by muscular pharynx.
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Digestion is extracellular in the intestine. Digested food is absorbed by the intestinal cells
Digestive system is simple straight tube.
Has mouth and anus
Annelida
Holozoic, saprophytic and parasitic (sanguivorous habit)
Feeds on small crustaceans worms, larvae and decaying matters and blood etc.
Extracellular (digestion like nereis and herudinea) inratcellular and intracellular digestion
(earthworm) are prominent features in annelida
Has a complete digestive system starting from mouth to ends at anus for all the class of
annelida
Digestive glands are found in the wall of the digestive tract.
Has well developed pharyngeal gland.
Crop in leech and gizzard in earthworm for breaking down the food, instead of stomach.
Arthopoda
Arthopoda shows great range of feeding habit.
This group of animals occupies wide range o habitats
They are holozoic in nutrition, but majority of them are omnivorous, carnivorous and
cannibalistic (who eats it same species).
They have well developed digestive system
Digestive gland is well developed and functional even in larval stage.
Digested foods are reabsorbed into the haemocel (coelomic fuid)
Digested food provide energy while some are store as fat
Animals are well equipped with extra appendages for catching the prey like chelated legs
maxillipedes and modified jaws are used for catching and directing prey to the mouth.
Digestion is extracellular
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Mollusca
Holozoic,havivorous and carnivorous some omnivore.
They feed on small animals insects, fishes, planktons and organic matter.
Mode of feeding is filter feeding.
Most bivalve collects their food by cilliary beating
Cilia are present in the gills filament
Food particles are directed towards the mantle cavity
The water current would lead toward the mouth.
Diffuse food into the blood and go into circulation
Digestion is intra cellular(Amoeboid cells digest food) and intercellular(cavity of
alimentary canal).
Has well developed digestetive system.
Echinoderm

Holozoic , carnivorous

Feeds on crustaceans, mollusks and fishes.

Has complete digestive system and digestive gland (open in mouth and ends in
anus)

Has stomach, pyrolic duct extended into flexible arm the form of pyrolic caecum

Pour the digestive juice, once digested it absorbed the food

Absorbed food is further digested intracelluarly and food is diffused int coelomic
fluid.

Coelomic distributes the food all over the body

Has well developed digestive system

Extratcellular digestion and intracellular digestation
Generalization of feeding mechanism in invertebrate
Generally the nutritional mode of different group of invertebrate varies significantly in
terms of feeding ingestion, absorption and egestion.
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Mode of obtaining food becomes more complex and specialized in higher groups of
invertebrate.
Absorption of digested liquid forms of feed in lower and solid and semisolid in higher
group.
Digestive system is completely lacks in lower group and found well organized digestive
system in higher vertebrate.
Digestion is normally intracellular to extracellular from lower organism to higher
groups.
Diffusion of digested food in lower vertebrate while in higher the food digested is
diffuse into the haemocoel, through it it is distributed to all over the body.
Trap their preys by pseudopodial extension, cilia and tentacles movement or bodily
movement in lower but in higher have specialized organs like arms in echinoderm and
mollusks.
Reference:
Armugum N.. (2004). A text book of invertebrate. Sara publication, new Delhi
Nemahelminthes/Aschelheminthe
General characteristics:
1. They are vermiform animals
2. They are bilaterally symmetrical
3. Body covered with cuticle
4. They are pseudocoelomate animals
5. They are parasitic or free living
6. The have organ system grade of organization
7. Excretory organ like protonephridia are present
8. Elementary canal is straight and has mouth and anus
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Classification
Phylum has five class;
1. Rotifer---------------- Rotaria
2. Gastrotricha--------------Chaetonotus
3. Kinorhyncha-------------Echinoderes
4. Nematomorpha----------Nectonema
5. Namatoda--------------Ascaris Lumbricoides(round worm),
a) Body is long, slender and large size round worm
b) Body has thick cuticle
c) Has sexual diamorphism
d) Digestive system is complete in adult
e) Circulatory system, respiratory system, cilia are completely absent
f) Excretory system consists of glandular organs nervous system consists of
circumenteric ring in anterior and posterior end
g) They are dioecious; male is small than female
h) Male has ventrally coiled tail
i)
Two penial specule is present
j) Fertilization is internal, and direct
k) Life cycle includes larval forms
l) They are parasitic in vertebrate
Annelida
General characters:

Soft cylidtcal and enlogated body

Bilaterally symmetrical body

Organ grade organization

Body covered with cuticle

Locomotion by the satae
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
Circulatory system is closed type

Excretory organ segmentally arranged nephridia is present.

Metamerically segmented body

Biltareally symmetrical

True coelomate,triplobastic

They are divided into 8 classes:

Polychaeta----------------------Nereis(sand or claw worm or rag worm)
Oligochaeta----------------------Pheretema Posthuma (earthworm)

Hirudinea-------------------------Hirudinaria granulose(leech)

Arcchiannelida

Echiuroidea

Sipunculoidea

Priapulida

Myzostomaria
Arthopoda:
General characteristics;
Body divided into three parts; head, thorax, and abdomen

2 pairs of Legs

2 pairs of wings

Pair of Antenna

Jointed legs
Divided into Five classes:
1. Merostomata
2. Arachinda------------------------Aranea(Spider), Plamnaeus(scorpion)
3. Crustacean------------------------saccullina(root headed barnacle), Penaeus(prawn)
4. Myriapoda-----------------------Spiroatreptus(millipede), Scolopendra(centipede)
5. Insecta----------------------------dragon fly, dung beetle and stick insect.
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