The only order of marine mammals in India other than the Cetacea, the order Sirenia, has just four species in two families worldwide. The two families are the Dugongidae, the dugong family, and the Trichechidae, or the manatee family. All the four species have become rare due to human exploitation for meat and oil. Steller’s Sea-cow, a large species belonging to this order, was wiped out of existence within years of its discovery in the 18th century.
All the sirenians are completely herbivorous and are confined to shallow waters of coastal areas where higher aquatic plant life is abundant. Dugongs are strictly marine mammals whilst manatees may live in the sea or in estuarine or riverine waters. Manatees can wriggle back to water if put on nearby land.
The manatees and the Dugong have no hind limbs. Their bodies are torpedo-shaped and they have flat tails with which they propel themselves in the water. Their forelimbs are paddle-like. The snout of the Dugong is down-turned, whilst that of the manatees is straight. All the sirenians have thick skin with little hair. Their eyes are small, round and lidless. The ears are tiny. Sirenians are very heavy-boned.
Manatees and dugongs generally live in groups. They must also come to the surface to breathe, just as whales and dolphins do. They may stay submerged for about 15 minutes between breaths. The mammary glands of the sirenians are located in the pectoral area, that is in the are in front between the flippers. It is believed that the myth of mermaids was inspired by the suckling of young ones held upright in a flipper. Sirenians live in groups for the most part.