The cells have a cylindrical or slightly ovoid cross-section, and their valves are only minimally silicified. C. pelagica forms chains, although these chains can sometimes break apart in preserved samples. The valve face features two conspicuous, winged processes that are easily visible under light microscopy. At the base of these processes, the valve is pierced by small slits, although these are seldom observable with light microscopy. Additionally, there is a central labiate process.