Out of all of the marine animals, the sea sponge definitely sounds the most innocuous. What’s so fearsome about a group of organisms who look like a pile of sticks and just hang out relatively motionless on the bottom of the sea floor? Following an expedition by researchers from the Monterey Bay Aquarium Research Institute (MBARI), four new species of “killer sponges” have been described. The paper comes from lead author Lonny Lundsten and was published in the journal Zootaxa.
Most sponges are filter feeders who dine on unicellular organisms floating through the water, but some need a little meatier of a diet. Carnivorous sponges have microscopic hooks covering their branch-like arms that help them catch larger prey, in a process that may be compared to a Venus fly trap. Once trapped, the sponges begin to devour the animal and can completely ingest it over the course of the next 10 days.
The sponges were discovered using cameras that skimmed the sea floor and some samples were carefully extracted for examination. When analyzing the samples so they could be properly detailed, Lundsten’s team noticed that there were several crustaceans trapped within the arms of the sponges and appeared to be decomposing.
This microscope image shows the carcass of a small crustacean (possibly a deep-sea amphipod) that was caught in the spines of one of the newly discovered carnivorous sponges, Cladorhiza evae. Image credit: Linda Kuhnz © 2013 MBARI.
Two of the newly-described species belong to the genus Asbestopluma, which contains the deepest-known sponges. Asbestopluma monticola was discovered atop an underwater volcano off the coast of Central California. Asbestopluma rickettsi was spotted in two Southern California locations, one of which was located next to a clam colony, though the researchers did not actually see any trapped prey.
Close-up view of Asbestopluma monticola, one of four new species of carnivorous sponges discovered off the West Coast of North America. Image credit: © 2006 MBARI.
Cladorhiza caillieti was discovered along the ridge of recent lava flow near Vancouver Island. Cladorhiza evae comes from a vent near Baja, California. Prior to this discovery, there were 35 known species and subspecies within the genus.
The manipulator arm on MBARI's remotely operated vehicle Doc Ricketts collects a Cladorhiza caillieti sponge growing on a piece of carbonate crust on the seafloor off the coast of Southern California. Image credit: © 2013 MBARI.
Though there is lots of evidence of carnivorous sponges consuming their prey, the event has not been witnessed as of yet. There is still much that remains to be known about carnivorous sponges, including exactly how many there are. The researchers note that “numerous additional carnivorous sponges from the Northeast Pacific (which have been seen and collected by the authors) await description, and many more, likely, await discovery.”
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