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"The blobfish had been sitting patiently on the ocean floor, mouth open waiting for the next mollusc to come through to eat," the pair said.

In the oceans, molluscs and crocodilians radiated into diverse new forms.

Academics said the find had challenged the belief that early molluscs, from a group known as Aculifera, were basic and primitive creatures.

The studies covered 50 species including land insects, fish, molluscs and corals -- some of the most biodiverse and most at-risk ecosystems on the planet.

Filter feeders are everywhere in the animal world, from tiny crustaceans and certain types of coral and krill, to various molluscs, barnacles, and even massive basking sharks and baleen whales.