Calantica eocenica was a stalked barnacle, a stationary crustacean that spent adult life cemented by a flexible stalk rather than walking or swimming. Its feeding limbs would have repeatedly opened into the current to collect plankton and other microscopic organic particles.

Although far less dramatic than a large crab or lobster, animals like Calantica were important members of the London Clay ecosystem. They occupied hard surfaces in a mainly soft-bottomed sea and converted suspended food into biomass that could then be eaten by larger animals.