Featured Research

from universities, journals, and other organizations

Five-limbed brittle stars move bilaterally, like people

Date:
May 10, 2012
Source:
Brown University
Summary:
Brittle stars and people have something in common: They move in fundamentally similar ways. Though not bilaterally symmetrical like humans and many other animals, brittle stars have come up with a mechanism to choose any of its five limbs to direct its movement on the seabed. It's as if each arm can be the creature's front, capable of locomotion and charting direction.

Why bother with turns or pivots? The brittle star doesn’t turn as most animals do. It simply designates another of its five limbs as its new front and continues moving forward.
Credit: Henry Astley/Brown University

Brittle stars and people have something in common: They move in fundamentally similar ways. Though not bilaterally symmetrical like humans and many other animals, brittle stars have come up with a mechanism to choose any of its five limbs to direct its movement on the seabed. It's as if each arm can be the creature's front, capable of locomotion and charting direction. Results appear in the Journal of Experimental Biology.

It appears that the brittle star, the humble, five-limbed dragnet of the seabed, moves very similarly to us.

In a series of first-time experiments, Brown University evolutionary biologist Henry Astley discovered that brittle stars, despite having no brain, move in a very coordinated fashion, choosing a central arm to chart direction and then designating other limbs to propel it along. Yet when the brittle star wants to change direction, it designates a new front, meaning that it chooses a new center arm and two other limbs to move. Brittle stars have come up with a mechanism to choose any of its five limbs to be central control, each capable of determining 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 -- they can be divided into matching halves by drawing a line down the center. In contrast, brittle stars are pentaradially symmetrical: There are five different ways to carve them into matching halves. Whereas bilateral symmetrical organisms have perfected locomotion by designating a "head" that charts direction and then commands other body parts to follow suit, radial symmetrical animals have no such 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're bilaterally symmetrical and reap the advantages of bilateral symmetry."

"For an animal that doesn't have a central brain, they're pretty remarkable," said Astley, the sole author of the paper.

Astley decided to study brittle stars after noticing that their appendages acted much like a snake's body, capable of coiling and unfurling from about any angle. Yet when watched brittle stars move about, he couldn't figure out how the individual arms were coordinating. "It was too confusing," said the fourth-year graduate student in the Department of Ecology and Evolutionary Biology. "There's no obvious front. There are five arms that are all moving, and I'm trying to keep track of all five while the (central body) disc was moving."

He decided to take a closer look, which, surprisingly, no other scientist had done. On a trip to Belize in January 2009 led by professor and department chair Mark Bertness, Astley plopped thick-spined brittle stars (Ophiocoma echinata) into an inflatable pool and filmed them. The animals were willing subjects. "They hate being exposed," Astley said, "so we put them in the middle of this sandy 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 side of the central arm then begins a rowing motion, much like a sea turtle, Astley said. The entire sequence of movement takes about two seconds. "They're pretty slow in general," Astley said.

To turn, the brittle star chooses a new center arm and the accompanying rowing arms to move it along. "If we as animals need to turn, we need to not only change the direction of movement, but we 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 body disk.'"

Oddly, the brittle star also chooses another type of locomotion -- that to bilaterals would appear to be moving backward -- about a quarter of the time, Astley documented. In this motion, the animal keeps the same front, but now designates the non-forward-rowing motion limbs to move it. The question, then, is why doesn't the brittle star define a new front and simply move forward? "There's clearly something that determines that," Astley said. "It could be the relative stimulus strength on the arms."

The research was funded by the private Bushnell Foundation.


Story Source:

The above story is based on materials provided by Brown University. Note: Materials may be edited for content and length.


Journal Reference:

  1. H. C. Astley. Getting around when you're round: quantitative analysis of the locomotion of the blunt-spined brittle star, Ophiocoma echinata. Journal of Experimental Biology, 2012; 215 (11): 1923 DOI: 10.1242/jeb.068460

Cite This Page:

Brown University. "Five-limbed brittle stars move bilaterally, like people." ScienceDaily. ScienceDaily, 10 May 2012. <www.sciencedaily.com/releases/2012/05/120510100345.htm>.
Brown University. (2012, May 10). Five-limbed brittle stars move bilaterally, like people. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2012/05/120510100345.htm
Brown University. "Five-limbed brittle stars move bilaterally, like people." ScienceDaily. www.sciencedaily.com/releases/2012/05/120510100345.htm (accessed July 31, 2014).

Share This




More Plants & Animals News

Thursday, July 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Visitors Feel Part of the Pack at Wolf Preserve

Visitors Feel Part of the Pack at Wolf Preserve

AP (July 31, 2014) Seacrest Wolf Preserve on the northern Florida panhandle allows more than 10,000 visitors each year to get up close and personal with Arctic and British Columbian Wolves. (July 31) Video provided by AP
Powered by NewsLook.com
Florida Panther Rebound Upsets Ranchers

Florida Panther Rebound Upsets Ranchers

AP (July 31, 2014) With Florida's panther population rebounding, some ranchers complain the protected predators are once again killing their calves. (July 31) Video provided by AP
Powered by NewsLook.com
Dangerous Bacteria Kills One in Florida

Dangerous Bacteria Kills One in Florida

AP (July 31, 2014) Sarasota County, Florida health officials have issued a warning against eating raw oysters and exposing open wounds to coastal and inland waters after a dangerous bacteria killed one person and made another sick. (July 31) Video provided by AP
Powered by NewsLook.com
Raw: Thousands Flocking to German Crop Circle

Raw: Thousands Flocking to German Crop Circle

AP (July 30, 2014) Thousands of people are trekking to a Bavarian farmer's field to check out a mysterious set of crop circles. (July 30) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins