Elasmobranchii is a subclass of Chondrichthyes, which includes sharks, rays, and skates. These marine animals are characterized by their cartilaginous skeletons, which are lighter and more flexible than bone. Elasmobranchs have a unique set of gills located on the sides of their bodies, allowing them to extract oxygen from water efficiently. Elasmobranchii are known for their diverse range of sizes and habitats, from the small dwarf lanternshark to the massive whale shark. They play crucial roles in marine ecosystems as predators and scavengers, helping to maintain the balance of ocean life.