Whale than males. Baleen whales have no teeth; instead they have plates of baleen, a fringe-like structure used to expel water while retaining the krill and plankton which they feed on. They use their throat pleats to expand the mouth to take in huge gulps of water. Balaenids have heads that can make up 40% of their body mass to take in water. Toothed whales, on the other hand, have conical teeth adapted to catching fish or squid. Baleen whales have a well developed sense of "smell", whereas toothed whales have well-developed hearing − their hearing, that is adapted for both
Baleen whale dislodge parasites. Some species of barnacle, such as "Conchoderma auritum" and whale barnacles, attach to the baleen plates, though this seldom occurs. A species of copepod, "Balaenophilus unisetus", inhabits baleen plates of whales in tropical waters. A species of Antarctic diatom, "Cocconeis ceticola", forms a film on the skin, which takes a month to develop; this film causes minor damage to the skin. They are also plagued by internal parasites such as stomach worms, cestodes, nematodes, liver flukes, and acanthocephalans. Before reaching adulthood, baleen whales grow at an extraordinary rate. In the blue whale, the largest species, the fetus grows