deposits in tissues and reduced ossification of bony structures. This reduced ossification of the skeleton (observed in some notothenioids) changes the weight and creates neutral buoyancy in the water, where the fish neither sinks nor floats, and can thus adjust its depth with ease. Physiology Notothenioids have a variety of physiological and biochemical adaptations that either permit survival in, or are possible only because of, the generally cold, stable seawater temperatures of the Southern Ocean. These include highly unsaturated membrane lipids and metabolic compensation in enzymatic activity. Many notothenoids have lost the nearly universal heat shock response (HSR) due to evolution at cold and stable temperatures. Many notothenioid fishes are able to survive in the freezing, ice-laden waters of the Southern Ocean because of the presence of an antifreeze glycoprotein in blood and body fluids. Although many of the Antarctic species have antifreeze proteins in their body fluids, not all of them do. Some non-Antarctic species either produce no or very little antifreeze, and antifreeze concentrations in some species are very low in young, larval fish. While the majority of animal species have up to 45% of hemoglobin (or other oxygen-binding and oxygen-transporting pigments) in their blood, the notothenioids of the family Channichthyidae do not express any globin proteins in their blood. As a result, the oxygen-carrying capacity of their blood is reduced to less than 10% that of other fishes. This trait likely arose due to the high oxygen solubility of the Southern Ocean waters. At cold temperatures, the oxygen solubility of water is enhanced. The loss of hemoglobin is partially compensated in these species by the presence of a large, slow-beating heart and enlarged blood vessels that transport a large volume of blood under low pressure to enhance cardiac output. Despite these compensations, the loss of globin proteins still results in reduced physiological performance. Systematics Naming Notothenioidei was first described as a separate grouping, as a "division" he named Nototheniiformes, by the British ichthyologist Charles Tate Regan in 1913., this subsequently has been considered as a suborder of the Percifomes. The name is based on the genus Notothenia, a name coined by Sir John Richardson in 1841 and which means “coming from the south”, a reference to the Antarctic distribution of the genus. Families This classification follows Eastman and Eakin, 2000 and includes references to additional classified species. Most species are restricted to the vicinity of Antarctica. Family