"Killer sponges" may sound like a bad B-grade horror film on the bottom of a double bill at the local drive-in theater in the 1950s, but they do exist -- and in fact four new species have been discovered on the deep seafloor of the Pacific Ocean, scientists say.
Lonny Lundsten, a marine biologist of the Monterey Bay Aquarium Research Institute in California, says the new species occupy deep, lightless pacific waters from the Pacific Northwest down to Baja California.
The first carnivorous sponges were discovered just 20 years ago, with only seven species now known in all the northeastern waters of the Pacific.
Unlike your basic kitchen sponge, the killer sponges look more like a small shrub with bare twigs, each "twig" covered with tiny hairs are microscopic hooks which the sponges use to trap small shrimp-like creatures such as amphipods.
In just a few hours the sponge's cells can engulf and digest the hapless victims, leaving nothing behind but an empty shell.
When some of the sponges were brought back to the Monterey labs, researchers discovered "numerous crustacean prey in various states of decomposition," Lundsten says.
Unlike the carnivorous species, most sponges are filter feeders, sustained by single-cell organisms and bacteria the sieve out of the surrounding shallow waters, using specialized whip-like cells called choancytes to create a continuous flow of water to bring its food source closer.
The carnivorous sponges have evolved to do without the choancytes, Lundsten explained.
"To keep beating the whip-like tails of the choancytes takes a lot of energy," he says. "And food is hard to come by in the deep sea. So these sponges trap larger, more nutrient-dense organisms, like crustaceans, using beautiful and intricate microscopic hooks."
One of the new species has been found on an extinct underwater volcano off the central coast of California, while a second was discovered in separate locations off the Southern California coast.
The third and fourth carnivorous species were found off Canada and Mexico, specifically on an underwater volcanic ridge offshore of Vancouver Island and off the southern tip of Baja California.
The current seven species count of "killer" sponges will likely increase in the future, the researchers say.
"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," Lundsten wrote in the journal Zootaxa.
