Some critters walk, while others swim, fly, creep, or crawl to get around. Not the stomatopod, though. This tiny, shrimplike marine animal from the Pacific beaches of Panama rolls. And it's the only known species in the animal kingdom that does.
So says Robert Full, an associate professor of integrative biology at the University of California in Berkeley, who has videotaped the strange cartwheeling crustaceans which were discovered by a colleague who brought several back to the United States for laboratory study.
Full says the creatures, whose Latin name is Nannosquilla decemspinosa, normally live in underwater burrows so cramped that they may have gradually learned to roll because evolution taught them that was the only way to turn around. Periodically waves or tides wash them ashore, and it is there, when surprised, that they arc their bodies tail-over-head into a ring and roll back to the safety of the water at a glacial 3.5 centimeters per second.
While the stomatopod can handle grades of 10 percent, it is unable to maneuver around obstacles and can only move in a straight line. It's in a free roll less than half of the time, according to Full's observations. The rest of the crustacean's time is spent generating power by pushing off with its head and tail, the same way we use our legs.
"The results of 350 million years of evolution tell us that wheellike movement is a possible but improbable method of locomotion on land," says Full, noting that the curious rolling facility could have some practical applications in locomotion mechanics for tiny robots. "By studying the mechanisms of locomotion and learning how the muscles and skeleton work--looking at exceptions to rules like this--we could get some biological inspiration for robotics."
