It’s the open ocean. A baby fish, less than a centimetre long, floats through the water, completely oblivious of the danger it is in. It’s caught in a current, but one so smooth that the fish cannot detect it. Its only clue to what’s happening comes too late, as it’s suddenly sucked into a ring of tentacles and swallowed by one of the ocean’s stealthiest predators – the sea walnut.

The sea walnut is a simple transparent blob, just a few inches long. It looks like a jellyfish but in fact, it belongs to a different but related group called the comb jellies, or ctenophores.

It’s not exactly a fearsome predator. It cannot see and it can only sense