A "two-chambered" system typically refers to an organism's heart structure, which consists of two distinct chambers: one atrium and one ventricle. This design is commonly found in certain species of fish, such as sharks and goldfish. The atrium receives deoxygenated blood from the body, while the ventricle pumps oxygenated blood to the gills for oxygenation. In contrast to more complex hearts, like those of mammals and birds that have four chambers, a two-chambered heart is simpler and less efficient in oxygen delivery. This structure is well-suited for aquatic environments, where oxygen is absorbed through gills rather than lungs.