The recently discovered harp sponge, Chondrocladia lyra, make not look like something you'd bring into the bathtub, but what it lacks in sponginess it more than makes up for in predatory behavior. The harp sponge uses those narrow spines to snare small fish and crustaceans, which it then digests whole.
Most sponges filter water for their food, but the carnivorous behavior of certain species of sponges was first described by Jean Vacelet and Nicole Boury-Esnault from the Centre of Oceanology at France's Aix-Marseille University 17 years ago. Since then, 24 members of the Cladorhizidae family of carnivorous sponges have been identified. The harp sponge, which was discovered in deep waters off the coast of California and found with particles of partially digested crustaceans embedded in its velcro-like spines, is described in the October 18th issue of Invertebrate Biology, and the Monterey Bay Aquarium Research Institute (MBARI) has kindly posted footage of this fan-like creature. Tragically, we don't get to see it snag any fishes, but we do get some lovely views and an explanation of the sponge's morphology.
The MBARI researchers believe that the sponge evolved its wide fan shape to maximize its predatory surface area, but the researchers were also keenly interested in the reproductive function of its vertical branches. Because cladorhizid sponges are found at such great depths (the harp sponge has been found at depths of 3300-3500 meters), researchers have had little opportunity to study their reproductive behavior. Harp sponges anchor themselves in soft, muddy sediment of the sea floor by their root-like rhizoids and need their spermatophores to do the traveling for them. Each of the sponge's vertical branches ends in a terminal ball that swells with packets of spermatophores. Eventually, the balls release the spermatophores, which will hopefully find another harp sponge to fertilize. That makes the branches something akin to mouth, stomach, and penis all in a single structure. It also means that if a fish swims too close to a harp sponge, it risks getting eaten, or getting an eyeful of sponge sperm.
New carnivorous harp sponge discovered in deep sea [Nature via reddit]