[Steve Frey]

Part 1

Sponges Get Respect

The next time you luxuriate in a tub with a piece of natural bath sponge resting on the soap dish nearby, consider this fact: One recently discovered species of sponge is a carnivore--adept at attacking, engulfing, killing and consuming flesh. Scientists discovered the species in 1994 in a Mediterranean marine cave about 12 miles from Marseille, France.

Asbestopluma hypogea has elongated filaments extending from a white oval body. Minute spikes of silica, called spicules, jut out from the filaments like tiny shards of glass. "The spicules act as hooks, so that small crustaceans are trapped as if the surface were Velcro," says marine biologist Jean Vacelet of the Marseille Oceanographic Center. Also, the sponge's cells can move around. And they do. "The cells of the sponge migrate as soon as the prey is trapped," Vacelet says. "After 24 hours, the prey is completely covered by sponge cells." The cells grab bits of meat, absorb them into their cytoplasm and move away to start digesting. The creature has no brain, no heart, no stomach, no muscles-- yet it is a voracious killer all the same. "The sponge is like a giant amoeba," adds Vacelet. But before you swear off scuba diving in the Mediterranean forever, be advised that he uses the word "giant" in relative terms: Asbestopluma is barely larger than your thumbnail. Scientists since Aristotle have wondered whether sponges were plants or animals. Indeed, if you don't look closely, you won't notice them doing much. "Sponges are the blobs of the animal world," says invertebrate biologist Sally Leys of the University of Queensland in Brisbane, Australia. "Every other animal has a nervous system." Not to mention muscles and a digestive tract. Even flatworms, clams and corals have these features, however rudimentary. Sponges, the oldest multi-celled animals on Earth, do not. Yet recent findings confirm not only that sponges are most assuredly animals but that they are quite accomplished ones at that. Though they occupy the bottom rung of the animal ladder, they can perform feats that would be amazing in higher animals, and scientists are now trying to understand how they do so. Like the "Blob" of the 1958 Steve McQueen movie, sponges can regenerate from small bits of tissue, even after being squeezed through a mesh. They can outcompete and outlive competitors among other inhabitants of rocky sea floors. They can brush off injury, send signals, shape-shift and produce the building blocks of possible anti-cancer drugs. Says Leys' Brisbane colleague and fellow sponge expert Mary Garson: "I think sponges deserve a lot more respect than they've gotten in the past." Close to 10,000 spe-cies of sponge populate the underwater world--in salt water and fresh water, in the tropics and off Antarctica, in the shallows of coral reefs and in trenches three miles down--though they are most plentiful and most colorful in shallows. Some are hollow globular structures big enough for a diver to hide in. Others are bouquets of hollow tubes. Some are mere incrustations on rocks, shells or blades of sea grass. A sponge's anatomy is unlike that of any other creature. Most sponges are covered by a slimy, leathery skin dotted with small pores that let in seawater--hence the phylum's scientific name, Porifera. The soft brown sponge we know from well-appointed kitchens and bathrooms is actually a chunk of collagenous skeleton, bereft of other tissue. (Don't be fooled. Cheap supermarket sponges are usually made of cellulose derived from plants.) Only certain kinds of sponge have skeletons this user-friendly. Most are embedded with spicules, which range from tiny chalky bars to glasslike needles and often give a dried skeleton the consistency of wall insulation.

Sponges Get Respect - page 2 | International Wildlife