Well, that's what scientists thought too. The stagnant water in the cave makes filter-feeding impossible, so sponges that live there have developed passive tentacles covered with microscopic, Velcrolike hooks. These hooks snag shrimplike crustaceans that happen to swim by. Within one day after capture, new tentacles envelop the unlucky victims, essentially burying them alive.
Digestion then begins.
The sponge's only known relatives live on the ocean floor.