Subclass Selachii is a scientific term used for the class of fish that includes sharks and rays. There are several other synonyms for this term, which are used interchangeably depending on the context. One of the most common synonyms is Elasmobranchii, which means "plate- gilled" and is derived from the fish's unique respiratory system. Another commonly used synonym is Selachimorpha, which is derived from the Greek words "Selache," meaning shark and "Morpha," meaning shape. Other synonyms for this subclass include Sharkidae, Galeomorpha, and Batoidea. Whichever term is used, there's no doubt that these fish are some of the most fascinating and awe-inspiring creatures in the ocean.