Post by Argo on Jan 18, 2006 3:31:45 GMT -5
Invertebrate can drop its stalk, flee predators
One of the more interesting groups of invertebrates, or animals without backbones, is the group known as the echinoderms.
Echinoderms usually have body parts that repeat in groups of five, known as pentamerous symmetry. They have a skeleton made of hard plates that interlock. Many members come armed with spines or other projections, thus giving the group its name "spiny skin."
This group of marine animals includes starfish, sand dollars, brittle stars and sea urchins. It also includes a lesser known class of animals known as the crinoids.
Although the crinoids are the least understood of living echinoderms, their skeletal remains are among the most abundant and important of fossils. More than 5,000 fossil species have been described.
The hard plates that make up their body are left behind at their death and become part of the sediment of the ocean floor.
There are, however, a number of species of living crinoids. One is the sea lily. This group is not well known by the average beach visitor because they tend to live in depths greater than 600 feet.
The sea lily resembles the flower that is its namesake. It has a stalk and a number of featherlike arms. It feeds by allowing small particles of living matter to land on its arms, then flicking food particles into a central food groove in the arm.
After a food particle is captured by a crinoid, it is wrapped in mucous and transported up the food groove toward the central mouth.
A second type of crinoid is the feather star. It looks much like the sea lily, but without the stalk. Many of the feather stars live at shallow depths. In the tropical Indo-Pacific Ocean, as many as 50 species of feather stars may inhabit a coral reef.
These animals are able to swim with their arms. However, it was believed that the sea lily did not move but remained rooted with its stalk to one place.
Tomasz Baumiller, University of Michigan professor of geological sciences, and Charles Messing of Nova Southeastern University Oceanographic Center found in their research that some sea lilies can move around.
They discovered that sea lilies can shed and regenerate the ends of their stalks. The researchers hypothesized that the sea lilies were shedding their stalks to leave one location, then attaching themselves to a new location with their arms.
The question that intrigued the two men was why would the sea lilies leave a location? Was there predation, perhaps by a fish? Or was there some sort of physical disturbance that made the substrate unsuitable for attachment?
Recently, while going through hundreds of hours of video shot by a submersible diving off of Grand Bahama Island more than 10 years ago, the researchers found an explanation for why the sea lilies might get up and go. The video showed sea urchins alongside the sea lilies. In some frames of the footage, stalks of the sea lilies littered the ocean bottom.
Other studies by Baumiller and Messing showed that the sea urchins take bites out of the living sea lilies, giving them a reason to drop their stalks and run away.
The technique of shedding their stalks and moving out of the area would be similar to the strategy of a lizard being captured by a bird. The lizard will release its tail that may be in the beak of a bird. While the bird is focused on the tail, the lizard will scoot away and can regenerate the tail over the next few months.
Likewise, while the sea urchin is preoccupied with the stalk, the sea lily can move to a new location, attach and grow a new stalk.
The rate of movement of the sea lilies is 4 to 5 centimeters per second -- about 100 times faster than thought earlier. In a race between a sea lily and a sea urchin, the sea lily would definitely win.
For more information, and a link to a short video of a sea lily crawling on the ocean floor, trailing its stalk behind it, you should visit www.newscientist.com/channel/life/dn8168.
www.charlotte.com/mld/observer/news/local/states/north_carolina/counties/catawba/13615333.htm
One of the more interesting groups of invertebrates, or animals without backbones, is the group known as the echinoderms.
Echinoderms usually have body parts that repeat in groups of five, known as pentamerous symmetry. They have a skeleton made of hard plates that interlock. Many members come armed with spines or other projections, thus giving the group its name "spiny skin."
This group of marine animals includes starfish, sand dollars, brittle stars and sea urchins. It also includes a lesser known class of animals known as the crinoids.
Although the crinoids are the least understood of living echinoderms, their skeletal remains are among the most abundant and important of fossils. More than 5,000 fossil species have been described.
The hard plates that make up their body are left behind at their death and become part of the sediment of the ocean floor.
There are, however, a number of species of living crinoids. One is the sea lily. This group is not well known by the average beach visitor because they tend to live in depths greater than 600 feet.
The sea lily resembles the flower that is its namesake. It has a stalk and a number of featherlike arms. It feeds by allowing small particles of living matter to land on its arms, then flicking food particles into a central food groove in the arm.
After a food particle is captured by a crinoid, it is wrapped in mucous and transported up the food groove toward the central mouth.
A second type of crinoid is the feather star. It looks much like the sea lily, but without the stalk. Many of the feather stars live at shallow depths. In the tropical Indo-Pacific Ocean, as many as 50 species of feather stars may inhabit a coral reef.
These animals are able to swim with their arms. However, it was believed that the sea lily did not move but remained rooted with its stalk to one place.
Tomasz Baumiller, University of Michigan professor of geological sciences, and Charles Messing of Nova Southeastern University Oceanographic Center found in their research that some sea lilies can move around.
They discovered that sea lilies can shed and regenerate the ends of their stalks. The researchers hypothesized that the sea lilies were shedding their stalks to leave one location, then attaching themselves to a new location with their arms.
The question that intrigued the two men was why would the sea lilies leave a location? Was there predation, perhaps by a fish? Or was there some sort of physical disturbance that made the substrate unsuitable for attachment?
Recently, while going through hundreds of hours of video shot by a submersible diving off of Grand Bahama Island more than 10 years ago, the researchers found an explanation for why the sea lilies might get up and go. The video showed sea urchins alongside the sea lilies. In some frames of the footage, stalks of the sea lilies littered the ocean bottom.
Other studies by Baumiller and Messing showed that the sea urchins take bites out of the living sea lilies, giving them a reason to drop their stalks and run away.
The technique of shedding their stalks and moving out of the area would be similar to the strategy of a lizard being captured by a bird. The lizard will release its tail that may be in the beak of a bird. While the bird is focused on the tail, the lizard will scoot away and can regenerate the tail over the next few months.
Likewise, while the sea urchin is preoccupied with the stalk, the sea lily can move to a new location, attach and grow a new stalk.
The rate of movement of the sea lilies is 4 to 5 centimeters per second -- about 100 times faster than thought earlier. In a race between a sea lily and a sea urchin, the sea lily would definitely win.
For more information, and a link to a short video of a sea lily crawling on the ocean floor, trailing its stalk behind it, you should visit www.newscientist.com/channel/life/dn8168.
www.charlotte.com/mld/observer/news/local/states/north_carolina/counties/catawba/13615333.htm