Friday, Oct. 4, 2002
* Japanese name: Torafunamako
* Scientific name: Holothuria pervicax
* Description: Despite their name, sea cucumbers are not plants but animals, close relatives of sea urchins and starfish. They are all echinoderms, and members of this group are radially symmetrical. This kind of symmetry is most familiar in the five-pointed shape of the starfish, but in sea cucumbers you can only see it if you chop one in half: Then you would see five strips of muscle inside the body wall, running from front to back. Sea cucumbers grow to anywhere between 2 cm and 2 meters long. They have many small, sucker-tube feet on which they feebly move across the ocean floor. The mouth is surrounded by 10 to 20 retractable tentacles.
* Where to find them: In the seas all around Japan. Sea cucumbers, like earthworms, are present in huge numbers, sometimes comprising 90 percent of the animal biomass of marine systems. In Japan they are eaten raw.
* Food: The diet of sea cucumbers is another way in which they resemble earthworms. Sea cucumbers feed on detritus -- dead pieces of plant and animal matter that accumulate on the sea bed. They are recycling machines, vacuuming mud and sand. "Processed" sand is passed out through the body.
* Special features: For unassuming animals, sea cucumbers have two amazing abilities. First, they can change their tissue structure from "fluid" to "solid," and back again. Echinoderm means "spiny skin," and reminds us of the hard spikes of sea urchins. But the spikes of sea urchins can turn from fluid form to solid form because they are made of a compound called collagen. This property allows sea cucumbers to squeeze easily into a crack in a rock, then wedge themselves in by solidifying their tissue. Predators (or Japanese fishermen) then have a big problem pulling them out. If they are caught in the open, they can use their second defensive ability -- to eject all their internal organs, including the gut, through their mouth or anus. The shock of such an eruption is often enough to make a predator change its mind about eating the animal. The empty body of the sea cucumber does not die, however: It regenerates its organs and continues to vacuum sand.