The blunt-spined brittle star (Ophiocoma echinata) doesn't let five limbs prevent it from walking like a human being.
This starfish cousin is radially symmetrical, meaning it's the same along several axes. Thus, it could theoretically use any combination of its five serpentine arms to move in any direction it wants. But instead, the brittle star designates one of its arms as its "front," and the remaining limbs propel it in that direction in a motion similar to a sea turtle's crawl on land—or even the way we ourselves walk. When the brittle star wants to change direction, it doesn't turn around. It simply designates a new front arm and coordinates the rest of its arms accordingly. The discovery, reported today in The Journal of Experimental Biology, marks the first time that a radially symmetrical animal has been found to move bilaterally, and it suggests the brittle star has developed the mechanism to enjoy the efficiency of bilateralism in spite of its anatomy. Not bad for an animal without a central brain.
ScienceNOW, the daily online news service of the journal Science
Video credit: Henry Astley