Scientists have discovered four new species of killer sponges living in the depths of the waters between the Pacific Northwest and Baja California.

Carnivorous sponges were first spotted by researchers around 20 years ago, and just seven species have been found in the northeastern Pacific, said a Monterey Bay Aquarium Research Institute news release.

The harmless-looking predators, which resemble twigs or brush and are covered with tiny hairs, trap small prey including amphipods and engulf them. A shrimp-like amphipod can be digested within a few hours by a carnivorous sponge, leaving just an empty shell.

Monterey Bay Aquarium Research Institute researchers discovered the killer sponges when they noticed "numerous crustacean prey in various states of decomposition" on some new sponge species they had collected.

One of the newly discovered species, Cladorhiza caillieti, was found on recent lava flows near a volcanic ridge off Vancouver Island. Along with another species, Cladorhiza evae, the collected sponge specimens were clutching a number of prey in their spines.

The two other new species, Asbestopluma monticola and Asbestopluma rickettsi, were found off the California coastline and are characterized by distinct spikes.

Publishing their findings in a recent paper, the study authors noted that they are eager to see the killer sponges in action someday and that more species are probably waiting to be found.

"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," the researchers wrote.

Unlike most sponge species, carnivorous sponges lack specialized cells called choancytes, which move to bring bacteria and single-celled organisms to the animal.

"To keep beating the whip-like tails of the choancytes takes a lot of energy. And food is hard to come by in the deep sea," study author and marine biologist Lonny Lundsten said in the news release. "So these sponges trap larger, more nutrient-dense organisms, like crustaceans, using beautiful and intricate microscopic hooks."

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