Underwater Britain: a hidden wonder

The UK has a rich diversity of marine wildlife and is home to more than 44,000 species from basking sharks to jellyfish and tiny corals.

But now a new species off ferocious predator that once stalked British waters has been unearthed.

The fossilised skull of a giant "sea monster" has been discovered off the UK's Jurassic Coast, a local council announced. The fossil comes from a pliosaur, which lived in the oceans 150 million years ago.

The skull, which was discovered by a local collector off the Dorset coast, measures 2.4m in length and scientists believe the creature would have been 16m in length - one of the largest pliosaurs ever found.

Pliosaurs were a form of plesiosaur, a group of giant aquatic reptiles which lived in the seas at around the same time dinosaurs roamed the Earth. They had short necks and huge, crocodilian-like heads that contained immensely powerful jaws and a set of huge, razor-sharp teeth.

They used four paddle-like limbs to propel their bulky bodies through the water, and would have preyed on dolphin-like ichthyosaurs and even other plesiosaurs.

The Pliosaurs were not the only creature to threaten British waters. As this gallery shows, there are modern day species which are threatening our native wildlife.

We take a look at the problems these and other new invasive species are causing as well as some of the existing species that live around Britain.