Many-legged creatures put best feet forward
Humans have four limbs - two arms, two legs - but in the animal kingdom there is far more variety.
Limbs are often moved by the contraction and relaxation of muscles.
The snail slides along on its single muscular foot at a top speed of 20 metres an hour.
Most birds stand on their toes so what we think of as their knee is actually an ankle, which bends backwards.
The tripod fish uses the long rays protruding from its pelvic fins and the single long ray from its tail fin to rest upon.
Although it has four legs, the kangaroo uses only its powerful hind legs to hop - at up to 60 kilometres an hour.
Most starfish have five limbs but some have as many as 50. Others have thousands of tiny tube-like feet.
In some insects, such as the grasshopper, elongated legs act as catapults, propelling the creature 200 times its own body length in one bound.
The springtail leaps along by snapping its spring-like tail, an extra elongated limb at its rear. The insect also has six real legs.
The spider has a hook on each of its eight legs to help it cling to its web. Despite having so many limbs, it can move with surprising agility.
WWF HK is a charity environmental organisation. Its mission is to build a future in which people can live in harmony with nature. Call 2526-1011 or e-mail http://www.wwf.org.hk