Fish vary greatly in size. The whale shark and basking shark exceed all other fish by a considerable margin in weight and length. Fish are a paraphyletic group that describes aquatic vertebrates while excluding tetrapods, and the bony fish that often represent the group are more closely related to cetaceans such as whales, than to the cartilaginous fish such as sharks and rays. [citation needed] As such, cross group comparisons on this page only serve a colloquial purpose.