WonderQuest with April Holladay, Article printer-friendly version

A provoked greater blue-ringed octopus. When disturbed, the octopus switches from its normal drab brown/yellow color to bright yellow with bold blue rings. [Courtesy of Roy L. Caldwell © Used with permission.]An octopus is cousin to slugs and snails

Q: Is an octopus a reptile, mammal, or amphibian? Or is it just a fish? (Christine, Chardon, Ohio)

Q: How do blue-ringed octopuses breathe? (Priscilla, Tootgarook, Victoria, Australia)

A provoked greater blue-ringed octopus. When disturbed, the octopus switches from its normal drab brown/yellow color to bright yellow with bold blue rings.  Courtesy of Roy L. Caldwell © Used with permission.

A: An octopus is not a reptile, a mammal, or an amphibian (though it can live short periods of time out of water — long enough to climb out of a tank at night and eat shell fish from other tanks). It is not even a fish.

The ancestors of octopuses branched off from the ancestors of vertebrates more than 550 to 600 million years ago. Annelids (for example, earthworms and leeches) and arthropods (insects, lobsters, and the like) may be their closest major related groups, says biologist Roy Caldwell, a professor at the University of California.

Octopuses are in the mollusk group — muscular slimy creatures such as slugs, snails, mussels, oysters, squids, and cuttlefish.

Although not fishes, all octopuses (including the blue-ringed octopus Reader Priscilla asked about) breathe like fish with gills. They suck water through two internal gills, just behind two of their three hearts. The gills extract oxygen and blow the water out through a tube, called a "siphon" or "funnel". The octopus can shoot through the sea — in reaction to the expelled water jet — although he usually walks or crawls.

When attacking prey, an octopus gets close, leaps forward by spurting a water jet backwards, and grabs his lunch — perhaps a crab or fish.

By the way, all octopuses have poisonous bites. The golf-ball size blue-ringed octopus of Australia, however, is the only octopus whose bite is known to kill humans. The poison can stop a person’s heart and breathing in several minutes. Without medical care, this can kill the victim. We have no antidote. With medical aid to maintain ventilation, though, victims usually recover.

There is another species, called Octopus mototi, whose name on the Rapa Island in the South Pacific, literally means "poisonous octopus," says Caldwell. We don’t know if this creature is deadly, "but I would not let one bite me."

Further Reading:

Do octopuses have teeth? WonderQuest

How long are an octopus' arms?  What is a siphon? Do octopuses have bones?  How did octopuses get so intelligent? Why don't octopuses have bones?  How do octopuses change colors? WonderQuest

Roy Caldwell, "Death in a Pretty Package: The Blue-Ringed Octopuses." Freshwater and Marine Aquarium Magazine, 23 (3): 8-18.

BBC: Octopuses

Related Lesson Plan, Courtesy of Discovery Education
(Click link for the entire plan)

The Amazing Ocotpus

Learning objective:  Some animals can change body color to blend in with their surroundings.  This ability both protects them from predators and allows them to sneak up on prey, since they are nearly invisible.

Grade Level: 3-5, 6-8

Topics: Animals: octopus and other cephalopod

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