Below is a list of the animals we know about. No one knows exactly how many species there may be altogether. New species are always being found and there may be tens of millions not yet discovered. Some experts think there may be millions of species of insects and at least a million species of deep – sea fish that no one has ever seen. About half of all known creatures and plants live in tropical rainforests. In a study of just 19 trees in a tropical rainforest, 1,200 beetle species were found. About 80 per cent of these had not been seen before. Arachnids 75,500 (spiders, scorpions, etc) Molluscs 70,000 (snails, clams, etc) Crustaceans 40,000 (shrimps, crabs, etc) Fish 29,300 Nematodes 20,000 (unsegmented worms) Flatworms 17,500 Segmented worms 12,000 Sponges 10,000 Birds 9,934 Jellyfish, coral, etc 9,000 Reptiles 8,240 Starfish 6,000 Amphibians 5,918 Mammals 5,416