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It appears that the brittle star, the humble, five-limbed dragnetof the seabed, moves very similarly to us. In a series offirst-time experiments, Brown University evolutionary biologistHenry Astley discovered that brittle stars, despite having nobrain, move in a very coordinated fashion, choosing a central armto chart direction and then designating other limbs to propel italong. Yet when the brittle star wants to change direction, it designatesa new front, meaning that it chooses a new center arm and two otherlimbs to move. Brittle stars have come up with a mechanism tochoose any of its five limbs to be central control, each capable ofdetermining direction or pitching in to help it move. The findings are published in the Journal of Experimental Biology. Many animals, including humans, are bilaterally symmetrical - theycan be divided into matching halves by drawing a line down thecenter. In contrast, brittle stars are pentaradially symmetrical:There are five different ways to carve them into matching halves.Whereas bilateral symmetrical organisms have perfected locomotionby designating a "head" that charts direction and then commandsother body parts to follow suit, radial symmetrical animals have nosuch central directional control. "What brittle stars have done is throw a wrench into the works,"Astley said. "Even though their bodies are radially symmetrical,they can define a front and basically behave as if they'rebilaterally symmetrical and reap the advantages of bilateralsymmetry." "For an animal that doesn't have a central brain, they're prettyremarkable," said Astley, the sole author of the paper. Astley decided to study brittle stars after noticing that theirappendages acted much like a snake's body, capable of coiling andunfurling from about any angle. Yet when watched brittle stars moveabout, he couldn't figure out how the individual arms werecoordinating. "It was too confusing," said the fourth-year graduate student inthe Department of Ecology and Evolutionary Biology. "There's noobvious front. There are five arms that are all moving, and I'mtrying to keep track of all five while the (central body) disc wasmoving." He decided to take a closer look, which, surprisingly, no otherscientist had done. On a trip to Belize in January 2009 led byprofessor and department chair Mark Bertness, Astley ploppedthick-spined brittle stars (Ophiocoma echinata) into an inflatablepool and filmed them. The animals were willing subjects. "They hatebeing exposed," Astley said, "so we put them in the middle of thissandy area and they'd move." To move, brittle stars usually designate one arm as the front,depending on which direction it seeks to go. An arm on either sideof the central arm then begins a rowing motion, much like a seaturtle, Astley said. The entire sequence of movement takes abouttwo seconds. "They're pretty slow in general," Astley said. To turn, the brittle star chooses a new center arm and theaccompanying rowing arms to move it along. "If we as animals needto turn, we need to not only change the direction of movement, butwe have to rotate our bodies," Astley explained. "With these guys,it's like, 'Now, that's the front. I don't have to rotate my bodydisk.'" Oddly, the brittle star also chooses another type of locomotion -that to bilaterals would appear to be moving backward - about aquarter of the time, Astley documented. In this motion, the animal keeps the same front, but now designatesthe non-forward-rowing motion limbs to move it. The question, then,is why doesn't the brittle star define a new front and simply moveforward? "There's clearly something that determines that," Astleysaid. "It could be the relative stimulus strength on the arms.". I am an expert from GZOUHE.COM, while we provides the quality product, such as Spa Facial Steamer , China Digital Therapy Machine, Portable Facial Steamer,and more.
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