Malpighian tubules : Organs of excretion in arthropoda are malpighian tubules. They are slender tubes normally found in the posterior regions of alimentary canal at the junction of the midgut and hindgut.

Closed type digestive system.

Birds have two pairs of limbs, forelimbs are modified into wings for flight.The wings are powered by the powerful flight or breast muscles attached to the large sternum of breast bone.Hindlimbs support the body and used for grasping, perching, wading and swimming

Internal shell-In Sepia(cuttle fish),Loligo(squid)
Shell absent-Octopus(devil fish)

Hydrostatic skeleton is a system of water-filled spaces that act as turgor operated chambers or valve for movements and pressure points

Parasitic platyhelminthes have a thick cuticle.They lack alimentary canal and absorb the nutrients directly through their body surface.Some parasites are provided with hooks and suckers.

Struthio (ostrich-a-flightless bird) and Ornithorhynchus (platypus-an egg laying mammal).

Parapodia for lateral,unjointed and paired appendages

Obellia,shows alternation if asexual and sexual phases in its life cycle.

Gas bladder or air bladder is a gas-filled sac present in fishes. It helps in maintaining buoyancy. Thus, it helps fishes to ascend or descend and stay in the water current.

The largest phylum is Arthropoda and its economic importance is as follows:
They are major agents for cross pollination. Insects, like butterflies and honey bee facilitate cross pollination.
Honey is an important food for human.
Many crustaceans, like lobsters and prawns are part of cuisine around the world.
The red dye cochineal, produced from a Central American species of insect, was economically important to the Aztecs and Mayans.
The blood of horseshoe crabs contains a clotting agent Limulus Amebocyte Lysate which is now used to test that antibiotics and kidney machines are free of dangerous bacteria, and to detect spinal meningitis and some cancers.
Maggots of housefly are used to treat those wounds which take time to heal because of absence of blood supply.
The relative simplicity of the arthropods' body plan, allowing them to move on a variety of surfaces both on land and in water, have made them useful as models for robotics.
They are carriers of many human parasite causing diseases like malaria, filaria and sleeping sickness.
Cockroaches are one of the major nuisance as they contaminate food in kitchens.
Termites are major causes of playing havoc with wooden furnitures.
Scorpions are known for their deadly sting, which can kill human and livestock.

Types of symmetry in animals

During the Jurassic period of Mesozoic era, certain gigantic reptiles roamed on land, swarm in water and flew in the air. these reptiles were called dinosaurs. These animals disappeared during a short time at the end of the cretacean period.
Their extinction occurred due to competition with early mammals or from climatic changes due to the collision must have produced huge dust clouds into air, screening sunlight from the earth. The lack of sunlight would have destroyed vegetation and cooled the atmosphere. These may be the reason for extinction of dinosaurs.
Reasons for successful adaptation on land by reptiles are
(i) Horny scales which reduce loss of water.
(ii) Internal fertilisation as gametes cannot survive on land.
(iii) Shell around the egg to check desiccation.
(iv) Fluid-filled amnion around the embryo to provide aquatic environment for development on land.

Key Features of Mollusca:
Molluscs are terrestrial or aquatic (marine or fresh water) having an organ-system level of organisation. They are bilaterally symmetrical, triploblastic and coelomate animals.
Structure. Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump. A soft and spongy layer of skin forms a mantle over the visceral hump. The space between the hump and the mantle is called the mantle cavity in which feather like gills are present. They have respiratory and excretory functions. The anterior head region has sensory tentacles. The mouth contains a file-like rasping organ for feeding, called radula. They are usually dioecious and oviparous with indirect development.

(a) Platyhelminthes are acoelomate, while Aschelminthes are pseudocoelomates. This indicates development of mesoderm.
(b) In Platyhelminthes both sexes are on the same animal, while in Aschelminthes there is segregation of sexes. This shows another point of evolution.

Parasites on Human Body
1. Taenia solium (Tape worm) Platyhelminthes.
2. Fasciola hepatica (Blood worm) Platyhelminthes.
3. Ascaris lumbricoides (Round worm) Aschelminthes.
4. Wuchereria bancrofti (Filarial worm) Aschelminthes.
5. Ancyclostoma (Hook worm) Aschelminthes.

The molluscs have advancement over annelids, as they have distinct head, better sense organs and gills or lungs for respiration.

The animals having bilateral symmetry move with a anterior end forward this has led to cephalisation i.e differentiate of a define head at the anterior end. cephalization involves concentration on nervous, tissue(brain) and sense organs in the head.
Thess arrangement is an asset in an adjustment in enviornment, has the anterior end of moving animal is first to encounter changes in the area it is entering.