Terri Lee Anson, age 11 , of Greenarood, Ind., for his question:
Is the octopus a fish?
The catfish is a true fish and so is the dogfish. But the starfish is not really a fish, and neither is the crayfish. The sea cucumber both live in the ocean, but only one of them is a fish. And the sea dwelling octopus is not even related to the true fish.
The octopus can live only in the salty waters of the sea. There are more than 25,000 different fishes in the teeming oceans. They share their world with thousands of other sea creatures that are not true fish. Their names sometimes fool us. The Jellyfish and the shellfish are not fish at all. The octopus is a distant cousin of the oyster, which is a shellfish. And no relative of the shellfish belongs to the fish family.
It seems odd that the octopus is related to a shellfish. For he has no crusty shell to protect his soft and tender body. This is the biggest problem of his life. Sharks and other hungry sea creatures can gobble him up with no trouble at all. So the long legged octopus spends most of his time hiding in rocky caves and crevices on the floor of the sea.
He comes out to hunt at night. When danger threatens, he scuttles back home in a hurry. He can creep along on his eight legs or walk on his eight toes. Or he can squirt out a Jet of water and spurt himself forward like a torpedo. He can also squirt out a jet of ink to cloud the water and scoot off to safety behind his homemade smoke screen.
A fish and an octopus are cold blooded sea creatures, and both have gills for taking oxygen from the water. But these things, say the experts, are not enough to class them as relatives. A fish, as you well know, is a bony fellow. The octopus has not a single bone in his body. Most fish have scales and fins. The octopus may blush with rosy gold or change his color from pasty white to speckled rays. But there are no scales on his tender skin, and he has no spiky fins.
The experts call him a cephalopod, which means head and foot. His eight legs grow in a ring around his mouth. Each leg, with its tapering toe, is fixed onto the head of the head footed cephalopod. The 400 different octopuses range from 1 inch to giants more than 9 yards long.
The cephalopod class is a branch of the huge tribe of the mollusks. Many of the soft bodied mollusks have shells to shield their tender bodies. The clams and oysters belong in a class of the mollusk tribe, the snails and slugs belong in another mollusk class. The octopus has some 40,000 mollusk relatives, but none of them are related to the true fish.