Animal Without Organs Digests Food on Its Body

Eating without having internal organs would seem to pose incredible challenges, but the marine animal Trichoplax has solved this challenge by digesting meals on top of its body, a new study finds.

The discovery, reported in the journal PLOS ONE, demonstrates that lack of neurons, muscles and bodily organs does not necessarily mean a creature is lacking in complex behaviors.

"Despite having only six cell types and lacking synapses, Trichoplax coordinates a complex sequence of behaviors culminating in external digestion of algae," lead author Carolyn Smith of the National Institutes of Health, and her colleagues Natalia Pivovarova and Thomas Reese wrote.

German zoologist Franz Eilhard Schulze first discovered Trichoplax in 1883. He noticed it moving along the walls of a seawater aquarium at the Zoological Institute in Graz, Austria. He described the small creature as resembling a hairy plate.

Since then, the species has been found all over the place: in the Red Sea, the Mediterranean, the Caribbean, off Hawaii, Guam, Samoa, Japan, Vietnam, Brazil, and Papua New Guinea, and on the Great Barrier Reef off the east coast of Australia, just to name a few locations.

It's since been determined that Trichoplax, defined as a marine metazoan, has just six cell types. Humans, in contrast, have about 200.

Using high tech electron microscopy and cell imaging, Smith and her team observed Trichoplax and its behaviors. They noted that the creature has cilia, which are minute, hair-like structures that line certain cells and beat in rhythmic waves. This helps the disk-resembling animal move.

Food, however, stops it in its tracks.

"When Trichoplax glides over a patch of algae," the researchers explained, "its cilia stop beating so it ceases moving."

A subset of one of the animal's cell types, lipophils, then secretes granules that break down the algae.

Read more at Discovery News