Class 11 Biology

Animal Kingdom


Joint Appendages

The presence of joint appendages is the reason for the name arthropoda. This is the largest phylum of Animalia and over two-thirds of all known species on the earth are arthropods.

Organ system level of organization is present. Body is bilaterally symmetrical, triploblastic, segmented and coelomate.


The body consists of head, thorax and abdomen. Body is covered with exoskeleton made up of chitin. Respiration is carried out by gills, book gills, book lungs or tracheal system. Open circulatory system is present. Sensory organs, like antennae, eyes, statocysts (balance organs) are present. Eyes can be compound or simple. Malpighian tubules are the excretory organs.



Most of the arthropods are dioecious. Fertilisation is usually internal and development can be direct or indirect. Most of them are oviparous.

Common Examples: Economically important insects – Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect) Vectors – Anopheles, Culex and Aedes (Mosquitoes) Gregarious pest – Locusta (Locust) Living fossil – Limulus (King crab).


Mollusca is the second largest phylum of Animalia. They are terrestrial or aquatic. The aquatic molluscs live in marine or freshwater habitats. Organ system level organization is present. Body is bilaterally symmetrical, triploblastic and coelomate.

Shell of Calcium Carbonate

The body is covered by a shell which is made up of calcium carbonate. Body is unsegmented with a distinct head, muscular foot and visceral hump. A mantle is formed over the visceral hump by a soft and spongy layer of skin. The space between the hump and the mantle is called mantle cavity. Feather-like gills are present in the mantle cavity. The gills facilitate respiration and excretion. Sensory tentacles are present in the anterior head region. File-like rasping organ, called radula is present in the mouth for feeding.



These are usually dioecious and oviparous. Development is indirect.

Common Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Seahare), Dentalium (Tusk shell) and Chaetopleura (Chiton).



Ehinodermates have an endoskeleton made up of calcareous ossicles. Due to this, the body is covered with spines. These are marine animals. Organ system level organization is present. Adults are radially symmetrical but larvae are bilaterally symmetrical. Body is triploblastic and coelomate. Digesive system is complete. Mouth is present on the ventral side and anus is present on the dorsal side.

Water canal system

It is the most distinctive feature of echinoderms. The water canal system helps in locomotion, capture and transport of food and respiration. Excretory system is absent.


These are dioecious animals. Fertilisation is usually external. Development is indirect. Larvae are free-swimming.

Common Examples: Asterias (Star fish), Echinus (Sea urchin), Antedon (Sea lily), Cucumaria (Sea cucumber) and Ophiura (Brittle star).



This phylum has a small group of animals which look like worms. Organ system level organization is present. Body is bilaterally symmetrical, triploblastic and coelomate. The body is cylindrical and consists of an anterior proboscis, a collar and a long trunk.

Open circulatory system is present. Gills are present for respiration. Proboscis gland is the excretory organ.

Reproduction: These are dioecious animals. Fertilisation is external and development is indirect.

Common Examples: Balanoglossus and Saccoglossus.