Pleuronectidae and they sink to the bottom. They are found on the bottoms of oceans around the world, with some species, such as the Atlantic halibut, "Hippoglossus hippoglossus", being found down to . The smaller species eat sea-floor invertebrates such as polychaetes and crustaceans, but the larger righteye flounders, such as "H. hippoglossus", which grows up to in length, feed on other fishes and cephalopods, as well. They include many important commercially fished species, including not only the various fish called flounders, but also the European plaice, the halibuts, the lemon sole, the common dab, the Pacific Dover sole, and the
Demersal fish benthic fish are denser, with negative buoyancy so they can lie on the bottom without any effort. Most demersal fish are benthopelagic. As with other bottom feeders, a mechanism to deal with substrate is often necessary. With demersal fish the sand is usually pumped out of the mouth through the gill slit. Most demersal fish exhibit a flat ventral region so as to more easily rest their body on the substrate. The exception may be the flatfish, which are laterally depressed but lie on their sides. Also, many exhibit what is termed an "inferior" mouth, which means that the mouth