Most people think sponges spend their days quietly sucking in and spitting out water, hoping to trap a few bacteria or some organic matter in their filters for dinner. A newly identified sponge may send this picture of passivity down the drain.
Jean Vacelet and Nicole Boury-Esnault of the Universite d' Aix-Marseille II in Marseille, France, discovered a sponge that has evolved some, shall we say, unique characteristics in response to the scarcity of food in the relatively still waters of the deep sea, they report in the Jan. 26 NATURE.
"This remarkable sponge is effectively a carnivore," Michelle Kelly-Borges of the Natural History Museum in London notes in an accompanying editorial.
The sponge has developed filaments to capture small crustaceans. Minute, hook-shaped, pointy structures called spicules cover the moveable filaments and provide "a Velcro-like adhesiveness," the authors say.
Crustaceans, usually less than 1 millimeter wide, get trapped on the spicules. They struggle for hours to free themselves. Then new filaments grow over the prey, covering it completely in a day. Within a few days, the sponge digests its catch.
Most of this food is broken down within the sponge's body, but the filaments can digest little nibbles, Vacelet explains.
The as-yet-unnamed sponge belongs to the genus Asbestopluma, which normally resides in the North Pacific and North Atlantic at least 100 meters below sea level. Indeed, members of this genus live as far down as 8,840 meters. However, Vacelet and Boury-Esnault found their specimen a mere 17 meters below sea level, in a Mediterranean cave.
No one knows for certain how the sponge got there. Perhaps strong currents carried it from a deep-sea canyon. In any case, the cave had all the attributes of the deep sea: cold water, limited nutrients, and darkness, Kelly-Borges notes.
Researchers had suspected that deep-sea and shallow-water sponges had different systems for capturing their dinner. Scientists had even seen sponges with spicules. However, they knew little about the deep-sea dwellers or what the spicules did.
The cave discovery "made it possible to observe for the first time how sponges feed in such extreme environments," the French scientists report.
Normal sponges "are filter feeders par excellence. Their entire body is organized for filtering water, which is moved inside an aquiferous system by choanocytes," or pumping cells.
The new sponge has neither choanocytes nor a system for filtering water. "The definition of the phylum, based on the aquiferous system and . . . choanocytes, is now inadequate," Vacelet says.
Gale Document Number:A16623373