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Its shell has chambers and the shell has even evolved to protect its brain. It has a brown and white shell on the outside. Their blood and nutrients are circulated throughout their body through a system of tubes, not just liquid everywhere.ĭo they have shells like other mollusks? Yes, cephalopods have shells. They also have a closed circulatory system. Some scientists say that octopi can even learn. That is very important if you are a hunter. Ganglia and small bunches of nervous tissue. They have ganglia that have fused to become a small brain. Maybe not so unique, but cephalopods have some other advantages that help them succeed. They let the tentacle grab onto creatures for food and hold rocks to help it move. An octopus tentacle also has special suction cups all over it. It sometimes has over 90 tentacles, short ones but many tentacles. There is a special cephalopod called a Nautilus. Squid usually have ten (10) and octopi have eight (8). They are the only creatures who use their tentacles as appendages. What makes them special? They have tentacles. An octopus will sneak up on you, grab onto you with a tentacle, and bite into your shell with its beak. Cephalopods are at the top of the invertebrate food chain. They are the most intelligent of any invertebrate, even compared to spiders and crustaceans. The basics are that they are mollusks like clams and snails but in a class called Cephalopoda (the cephalopods).