Friday, May 25, 2001
A reader writes, "I know that starfish have
amazing powers of regeneration, but I have seen pictures of regenerated
starfish and in some the regenerated arms are much smaller than the
original arms. I read that regenerated arms never grow as big as the
originals and my question is: Would the starfish's ability to move and eat
be affected by this?"
My reader read wrong. Regenerated arms of most starfish
grow as big as the originals. It just takes time, perhaps a year or more,
before the reformation is complete.
During that time, a shortened limb might not be quite
as efficient as a full length one, but starfish adapt. Some commonly have
only one limb and do just fine.
The most famous of these one-armed creatures are known
by their scientific name, Linckia (LIN-kee-a). This name was chosen in
honor of J. H. Linck, an early naturalist who published an article on
starfish in 1733.
Linckia starfish are common in Hawaii and other parts
of the Pacific. Most textbooks discuss them in detail because, unlike
other starfish, they can cast off an arm without any part of the central
body attached and that arm will slowly grow into a complete starfish.
This new individual begins life with four tiny arms
budding from the end of the cast-off stump. Because the shape resembles a
shooting star, Linckia at this stage are called comets. Comets are a
common sight on Hawaii's reefs.
Some starfish can replicate themselves from only one
arm and about 1/5th of the central disk, the "body" of the
creature, and others divide their central disk in two. Each half then
regenerates its missing parts.
Starfish also reproduce the usual way, with sperm and
eggs. Once a year, males shed their sperm and the females their eggs into
the water. If they find one another, fertilization takes place and the
resulting tiny creatures become part of the ocean's drifting animal life
Eventually, the little stars settle on the ocean floor.
It can be hard to make heads or tails out of starfish
because they don't have either. They do, however, have sides, a top side
and a bottom side. At the center of the top is the creature's anus; the
center of the bottom is an efficient mouth.
This voracious mouth is the reason we don't see usually
starfish in aquariums: These creatures eat just about anything and can
wreak havoc in a home aquarium.
One starfish species can locate buried prey, then dig
down and catch it.
Others have tiny pincers that rise from their backs and
grab hold of small fish, snails or crabs that have the bad luck to rest
Starfish also eat spiny sea urchins, sponges, anemones,
clams and oysters.
To eat two-shelled animals, the star pulls the shells
pulls apart with its arms, inserts its stomach into the opening and
When you hold a starfish, it doesn't seem as if this
thing could dig up, hold or pull apart anything. But when threatened
starfish withdraw their suction-cup feet on their underside and stiffen
their skin on the topside.
After you put the starfish down, it softens up and
walks off. Some starfish walk into big trouble. The one called
crown-of-thorns locates corals by smell, creeps over to them and starts
eating. When these starfish are thriving, they can devastate coral reefs.
There's controversy about how to get rid of
crown-of-thorns starfish during a bloom, or if we should even try. But
there's one thing everyone agrees on: Never cut them up and leave the
pieces in the water.