By Karl Gruber

They don’t exactly say achoo, but sponges can “sneeze,” according to a new study that shows the simple aquatic creatures are more complex than previously thought.

Sponges are stationary animals, found in both marine and fresh water, that lack nervous and digestive systems. The porous invertebrates have a central cavity called an osculum, where wastes are released into water and then washed away. Not much of an exciting agenda. (Watch a video of the sponge sneezing.)

But there’s more there than meets the eye. Scientists have shown that sponges can respond to their environment thanks to a bunch of fixed, fingerlike structures called cilia, located within the osculum. (See “Antarctic Glass Sponges Live Life in Fast Lane.”)

Humans also have cilia that are used in sneezing: When we breathe in foreign particles, sensors in our noses and sinuses detect the particles. The sensors signal the cilia—tiny, hairlike paddles that line our nostrils and sinuses—to move to expel the irritants.

When these “fingers” detect something odd, like chemicals in the water, they send a signal to make the sponge contract its whole body in a sneezelike behavior that jets out water and chemicals.

“When I first began experiments for this study, I was quite surprised with just how responsive sponges are to their environment—sometimes even the slightest vibration would cause the sponge to sneeze!” said study co-author Danielle Ludeman of the University of Alberta.

Rethinking Brain Evolution

The finding is unexpected, experts say, since sponges don’t have a single sensory cell.

“This is a very exciting and comprehensive study that clearly demonstrates that sponges are more sophisticated,” said Gert Wörheide, a sponge-evolution expert from Ludwig-Maximilians University in Munich, Germany, who wasn’t involved in the study, published January 12 in the journal BMC Evolutionary Biology.

In fact, the cilia may serve as a kind of sensory organ for the primitive sponge—possibly the first instance of complex sensory systems in evolutionary history. (See pictures of strange-looking sea creatures.)

Discovering such a sensory system in a primitive animal like the sponge may also shed light on the evolution of the brains of other organisms, scientists say.

“The sneeze is a delightful behavior,” said study leader Sally Leys of the University of Alberta, “and one that is a great tool for understanding how coordination systems may have arisen during the evolution of early multicellular animals.”