This supports the idea that they survived by absorbing carbon and oxygen dissolved in the surrounding seawater. After all, they didn’t seem to have any active body parts. Even stationary filter-feeders like barnacles use sieves to strain food from the water. Corals have stinging cells—tiny harpoons that impale their prey. Even sponges have small hairs that pump water through their inert bodies. But rangeomorphs showed no trace of any of these active feeding structures. They may just have sat there, waiting for stuff to diffuse across their expansive surfaces. Feeding was more like something that happened to them, rather than something they actively did.