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Animals that glow in the dark first appeared much earlier than previously thought, new research suggests.

Scientists think that an ancient group of marine invertebrates - called octocorals - may have been the first animals to glow, more than 500 million years ago.

This pushes back the previous oldest dated example by nearly 300 million years.

Animals that glow use the ability for a huge range of reasons including camouflage, communication and hunting.

The name given to the ability of living things to produce and give out light is bioluminescence.

There are many different bioluminescent animals - including species of fish, worms, fireflies, sharks and jellyfish.

The light these creatures produce is created inside their bodies by chemical reactions - meaning they are able to glow in complete darkness.

Until now, the first glow-in-the-dark creatures were thought to be small marine crustaceans called ostracods, which lived around 267 million years ago.

However, a new study by experts in America says that ancient group of marine invertebrates called octocorals - which includes soft corals - were actually the first.

Andrea Quattrini, curator of corals at the Smithsonian's National Museum of Natural History in the US, and senior author on the study, said: "Nobody quite knows why it first evolved in animals."

Lead author Danielle DeLeo explained: "We wanted to figure out the timing of the origin of bioluminescence, and octocorals are one of the oldest groups of animals on the planet known to bioluminesce."

The team looked at data using 185 species of coral and their research suggested that 540 million years ago the common ancestor of all octocorals were very likely bioluminescent.

Scientists added that they think bioluminescence had played an important role in the evolution of the octocoral species.