Seals have a slick, streamlined, torpedo-shaped body which makes them among the world's best divers. Millions of years of adapting to the sea has modified their four limbs into flippers. The various seal species differ size and weight. The smallest seal is the ringed seal of the Arctic, which is about 1.5 metres long and weighs up to 90 kg. The largest earless seal is the southern elephant seal, which weighs about 3,600 kg and can grow up to 6 m long.
Sea lions are the biggest of the eared seals.
Male seals are generally much larger than the females. Seals can see and hear well but have a poor sense of smell. Most pinnepids have a covering of short hair which they shed every year. Only the walrus is almost bare-skinned. Their bodies are padded with fatty blubber that acts as an energy store and provides insulation against the cold.