Snails belong to the phylum Mollusca which moves very slowly with the help of a muscular foot that is present under its belly. The muscular foot is a thick structure in snail which comes out of an opening in the shell during movement. The muscles in the foot contract and relax and it makes wave-like movements and produces a slimy substance called mucus. A trail of mucus is left behind when a snail crawls on a surface. The shell is dragged along with the foot.

The fish has a streamlined body that tapers at both ends which helps to reduces water resistance and makes it easier for the fish to swim in the water. A fish has fins and tail, which help it to swim inside water. The dorsal, pelvic and anal fins help in balancing the body of a fish, while the pectoral fins help a fast-moving fish to suddenly stop. The fishtail with its fin works like a rudder to a boat. The fish skeleton is covered with muscles that make the front part of the body curve to one side and the tail part swings on the opposite side, thus, curving the fish’s body while swimming. Then, immediately, the body and the tail of the fish curve to the other side, giving a jerk and pushing its body forward.

Birds have wings and feet, so they can fly and walk. Each part of a bird is adapted for flight. Birds have a streamlined body that reduces air resistance. They have hollow bones that make them light. Their forelimbs are modified into wings that are covered with feathers. Their strong chest muscles which help in moving wings up and down. The breast bones of birds are modified to hold flight muscles which help in moving wings up and down. Birds hindlimbs bones help in walking and perching. Birds are the only creatures to have feathers that help them to fly. They have two kinds of flight feathers—the wing feathers and tail feathers. Birds spread out their wings when they glide or soar and are flapped up and down. Flightless birds have larger and well-developed legs, but they have reduced wings. The upward movement during the flapping of wings is called upstroke. The downward movement of the wings is called downstroke. The tail feathers balance the bird when it lands, perches on a branch or walks on the ground. They also allow it to change direction when in the air.