Squid and Octopi - Smart CephalopodsHere are the smart ones. Octopi mainly. They rock. The basics are that they are mollusks like clams and snails but in a class called Cephalopoda (the cephalopods). They are the most intelligent of any invertebrate, even compared to spiders and crustaceans. They are hunters. Cephalopods are at the top of the invertebrate food chain. An octopus will sneak up on you, grab onto you with a tentacle, and bite into your shell with its beak.
With TentaclesWhat makes them special? They have tentacles. That will be the first thing you notice. They are the only creatures who use their tentacles as appendages. Squid usually have ten (10) and octopi have eight (8). There is a special cephalopod called a Nautilus. It sometimes has over 90 tentacles, short ones but many tentacles. An octopus tentacle also has special suction cups all over it. They let the tentacle grab onto creatures for food and hold rocks to help it move.
And GangliaMaybe not so unique, but cephalopods have some other advantages that help them succeed. They have ganglia that have fused to become a small brain. Ganglia and small bunches of nervous tissue. Cephalopods are smarter. That is very important if you are a hunter. Some scientists say that octopi can even learn. They also have a closed circulatory system. Their blood and nutrients are circulated throughout their body through a system of tubes, not just liquid everywhere.
And Tiny Shells InsideDo they have shells like other mollusks? Yes, cephalopods have shells. A Nautilus is easy. It has a brown and white shell on the outside. An octopus is a little harder. Its shell is inside of its body. Its shell has chambers and the shell has even evolved to protect its brain. That protection is an advantage. It's also an advantage for the octopus to have the shell inside of the body. It can move around easier and get into tight places to capture prey.
Chambered Nautilus (National Aquarium Video)
Encyclopædia Britannica (Octopi):