The Sea Lily vs. The Sea Urchin

Throughout evolutionary history, animals have been evolving to better adapt to their environments. They have changed in ways that will better allow them to hide from and escape from predators, hide from and attack prey, and ways that have made reproduction more efficient. Marine animals are no exception.

Sea lilies have adapted to the fact that they are preyed on by sea urchins. If they sense a predator in the area, they can “shed their stalk ends like lizards’ tails and scoot away.” This is a very interesting find because it was originally thought that sea lilies were sessile and that they could not move from where they were anchored to the substrate. In studying fossils of crinoids, which is what a sea lily is, researchers found that similar marks from sea urchin “mouths” were found on the fossils that they found in current research. They concluded that this escape mechanism was derived from predation pressures and that it is a development that probably occurred only about 150 million years ago. Evolution is interesting! If you would like to read the full article click here.

Sea urchin growth

Researchers Amy Johnson and Olaf Ellers are studying how sea urchins (and echinoderms in general) can grow. Somehow, they can do it without having to shed their shells or skeletal plates.

They discovered that as urchins grow, the collagenous tissue inside, outside, and between their skeletal plates softens. The shell inflates like a balloon. The collagen stretches and expands gaps between the plates from the inside, while containing them from the outside. Eventually, the tissue between the plates is reabsorbed and is replaced by hard shell. This mechanism is similar to the growth of a vertebrate skull. [1]

Scientists want to use this information to make “sea farms” of sea urchins possible. Only two experimental hatcheries are in use right now: a commercial one in Lubec, Maine, and another developed by the University of New Hampshire. If they are successful, they could “seed” areas overharvested for sea urchins to restore their populations. (Sea urchins are a delicacy in Japan. In 1993, 30 to 40 million pounds were harvested.)

They are still looking into what makes sea urchins reproduce, grow, and thrive. This research is complicated by the fact that it takes sea urchins six years to reach sexual maturity.
Right now they aren’t sure yet if sea urchin sea farms would be economically viable.

[1] Bowdoin Researchers Seek Methods to Spur Sea Urchin Growth
http://www.bowdoin.edu/news/archives/biology/000222.shtml

Sea urchins enter the genetic spotlight

Sea urchins are really quite awesome.

The California purple urchin (Strongylocentrotus purpuratus)
http://www.brown.edu/Administration/News_Bureau/2006-07/06-052.html

Not only do they look really cool, but they are our closest invertebrate relatives on the ol’ evolutionary tree, genetically speaking. Good thing too, now that the entire genome has been coded for humans and sea urchins. This revealed that sea urchins are actually more closely related to us genetically than fruit flies.

Professors Gary Wessel and Sorin Istrail at Brown University plan to use this information in research on Huntington’s disease and muscular dystrophy.

They found a few surprises along the way, too. Apparently, sea urchins have a very sophisticated innate immune system. They also have genes associated with taste and smell, hearing and balance. They even have a robust gene set for visual perception…on their feet!
“I’ve been looking at these organisms for 31 years – and now I know they were looking back at me.” says Gary Wessel.

These echinoderms live on rocks and shells in the saltwater of low-tide to deeper water (up to 750 feet) areas. They mostly eat green algae, and move around on their small tube feet.

See also: Braccini, S. 2001. "Arbacia punctulata" (On-line), Animal Diversity Web. Accessed February 20, 2010 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Arbacia_punctulata.html.