Live Science reports:

A sea animal so simple that it looks like a blobby pancake may hold the secret to the origin of neurons.

Placozoans are one of the five major branches of animals, along with bilaterians (which include everything from worms to humans), cnidarians (corals and medusas), sponges and ctenophores (comb jellies). They’re the most basic of the bunch, consisting of millimeter-long blobs of cells without organs or body parts. They move through the water using cilia — tiny hair-like structures — absorb nutrients by engulfing particles, and reproduce by simply budding off new offspring.

Placozoans diverged from other animals about 800 million years ago, and just a few species are known. But new research has found that these unassuming creatures may hold the key to the eventual evolution of the nervous system. Placozoans, it turns out, contain cells that show striking similarities to neurons, even though they are nowhere near as complex.

“Our results fit into the idea that neurons are a very complex cell type that has evolved in a gradual way,” study author Xavier Grau-Bové, a postdoctoral researcher at the Centre for Genomic Regulation in Barcelona, told Live Science. “We are maybe seeing the remnants of something that, when we diverged with placozoans, was sort of an ancestral neuron with likely a different function.” [Continue reading…]