classification of invertebrates

Those animals which have no backbone or vertebral column are called invertebrates. They are classified into nine phyla. Characteristics of the animals of these phyla are given below:
1. Phylum: Protozoa
i. They are unicellular organisms.
ii. They are mostly found in water.
iii. These animals have pseudopodia, flagella or cilia for locomotion.
iv. They can be free living or parasitic.
Some examples: amoeba,paramecium etc

2. Phylum: Porifera
i. Porifera means pore bearer animals, commonly called sponges.
ii. Most of them are marine organisms except spongilla.
iii. They are diploblastic animals.
iv. They respire through general body surface.
V. They do not move from place to place, so they are called sessile.
vi. The presence of calcium and silicon makes their body rigid and strong.
vii. Sponges have two types of openings on their body surface i.e. ostia(mouthlets) and osculums(anus).
Some examples: sycon, spongilla,euspongia etc.

3. Phylum: Coelenterata
i. The body of the coelenterate have a hollow cavity called coelenteron.
ii. They are diploblastic animals.
iii. The mouth serves for both ingestion and ejection.
iv. They have tentacles around their mouth which help for locomotion and capturing of prey.
v. They have stinging cells called cnidoblast.
vi. They reproduce by both asexual and sexual methods.
Some examples: hydra, coral, jellyfish, obelia etc.

4. Phylum: Platyhelminthes
i. They are also called flat worms. Their body is soft. They are flat either like a leaf or a tape.
ii. Alimentary canal is incomplete.
iii. They are hermaphrodites( their body contains both male and female reproductive organ).
iv. They are motly parasites.
v. Their body is unsegmented.
vi. They are triploblastic animals.
Some examples: liverfluke, tapeworm, planaria etc.

5. Phylum: Nemathelminthes
i. They are commonly called round worms. Their body is cylindrical and unsegmented.
ii. Alimentary canal is complete.
iii. Their body is bilaterally symmetrical.
iv. They are nuisexul.
v. They are reproduce by the sexual method only.
vi. They are mostly parasitic but some are free living too.
Some examples: ascaris, hookworm, pinworm etc.

6. Phylum: Annelida
i. They are mostly aquatic and some are tereestrial.
ii. They have cylindrical, segmented and elongated body.
iii. They respire through skin.
iv. They are usually hermaphrodires while some are unisexual.
v. Their digestive system is complete.
vi. Locomotory organs are called setae.
Some examples: earthworm, leech etc.

7. Phylum: Arthopoda
i. Their body is segmented and divided into head, thorax and abdomen.
ii. Their body is covered externally with exoskeleton.
iii. They have limbs or appendages with joints.
iv. Their mouth parts are well developed for chewing, piercing and sucking.
v. They have compound eyes.
Some examples: crab, scorpion, housefly, millipede, spider etc.

8. Phylum: Mollusca
i. Their body is divided into head, visceral mass and foot.
ii. They are unisexual.
iii. They are found both on land and in water.
iv. They have soft body which is usually covered with a hard shell.
v. They have well developed organs system.
Some examples: snail, slug, octopus etc.

9. Phylum: Echinodermata
i. They are found in sea water.
ii. Their body is covered with spiny hard skin made up of calcareous shell.
iii. They do not have a distinct head.
iv. They are unisexual.
V. They have tube like feet for locomotion.
vi. The body is divided into oral and aboral sides.
Some examples: star fish, sea-lily, sea-urchin etc.