Before the K–Pg boundary, plankton skeletons — which experts refer to as 'coccospheres' — found in the fossil record looked notably different to those preserved from after the catastrophe, the team said. A large hole in the coccospheres from after the mass extinction suggests that the microorganisms had flagella — thin, tail-like structures, whose whipping motion would have allowed the algae to swim around and grab bacteria with its 'haptonema'