Coelacanth (c) Peter Scoones/Getty Images
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Mission to study 'living fossil'

An international team of researchers is setting out tonight on an expedition to dive in the deep sea caves of South Africa in a bid to locate an extremely rare and unusual fish that is said to be a living fossil.

The coelacanth has existed unchanged for almost 400 million years, and the biologists will have to dive to depths of more than 100m to reach it.

They will attach acoustic tracking devices to the fish in order to study their behaviour, and plan to capture 3D moving images of their fins as they swim.

In this short clip, expedition leader Laurent Ballesta from the French organisation Andromede Oceanology explained why coelacanths were so important to science.

Coelacanth footage from BBC documentary Life on Earth