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Ocean Watch

During my husband's recent sailboat adventure in Australia, we kept in touch by e-mail. Craig doesn't write your average love letters. His first one said, "I saw a story in a Sydney paper about a new species of octopus that mimics sea snakes, lionfish and other dangerous critters. It's very cool."

Craig came home the next week with dirty clothes mixed thoroughly together with clean clothes inside his duffle bag. But I forgave him his laundry shortcomings when he handed me a ragged piece of newspaper reporting an astonishing story about a new kind of octopus.

Australian researchers recently announced their discovery of an octopus in Indonesian waters that, when threatened, takes on the appearance of poisonous animals. For instance, when territorial damselfish pester a foraging octopus, it takes on the appearance of a banded sea snake, which eats damselfish.

This octopus can also transform itself into a lionfish with bannered, toxic spines extended. If that doesn't suit the occasion, the octopus can mimic the banded sole, a flatfish species common in the area also bearing poisonous spines.

How does a spineless octopus transform itself into the shapes and colors of such diverse creatures? Ingeniously. To look like a sea snake, the octopus hides six of its eight arms inside a hole in the sand while stretching the remaining two in opposite directions. Then the octopus changes color to match those of the snake.

To resemble a flatfish, this octopus uses jet drive. Propelling itself forward with head extended, the creature molds its trailing arms into the leaflike shape of a sole. The octopus then undulates its body along the bottom like a swimming flatfish.

An octopus taking on the appearance of a lionfish swims just above the sea floor with arms extended like the flared spines of this lovely but noxious fish.

This newly discovered octopus has an open arm span of about 2 feet across and lives on silt and sand bottoms off river mouths in six to 35 feet of water. There, the octopus preys on creatures such as sea urchins, crabs and fish.

Many of these types of bottom-dwelling animals dig tunnels and make mounds in the soft sea floor of delta areas. Nearly all types of octopuses sit at the mouths of such tunnels, or on top of mounds, waiting for their occupants to venture out. Sometimes, octopuses also crawl along the bottom, sticking their suckered arms down holes to grab their prey.

The new Indonesian mimic octopus does these things, too, but it also has another, unique method of hunting. Researchers have seen this octopus entering a tunnel through one hole and emerging from another hole up to three feet away. No other octopus enters its prey's homes like this.

This new octopus' behavior is remarkable, but it's not surprising that it was found in this family of invertebrates. Octopuses and their kin are smart, and many can instantly change both the color and texture of their skin. One type of squid matches the colors of parrotfish, enabling it to swim unnoticed among those algae-grazing fish and then surprise its prey.

This new octopus is the only one ever seen posing as another animal in the absence of that animal. Besides that, this intelligent creature decides which animal to mimic, depending upon the circumstances.

Craig couldn't have brought me a better gift from Australia than that octopus article. His e-mail said it perfectly: It's very cool.