THE FRILLED SHARK

In the dark waters of the deep sea, lurk many curious and enigmatic animals that few have seen.

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Frilled sharks (Chlamydoselachus anguineus), for instance, have been known about for more than a century, but much of their lives remain mysterious.

We know what they look like from the occasional specimens that are hauled up in deep-sea fishing nets around the world. Most of their 2m-long (6.5ft) brown or grey body is a smooth, finless tube, with a dorsal fin far down on the back, near the trailing, ribbon-like tail.

The strangest features are up at the head end, however. Frilled sharks have six large gill slits – one more than most sharks. In fact, there are only five other living species in the frilled shark's taxonomic order, the Hexanchiformes, which includes sixgill and sevengill sharks.