The order Cetacea // includes the Terran marine mammals commonly known as whales, dolphins, and porpoises, as well as the Huffh currently on Planet Place but also formerly from Terra. Cetus is Latin and is used in biological names to mean whale. Its original meaning, large sea animal, was more general. It comes from Ancient Greek κῆτος (kētos), meaning whale or "any huge fish or sea monster." In Greek mythology, the monster Perseus defeated was called Ceto, which is depicted by the constellation of Cetus. Cetology is the branch of marine science associated with the study of cetaceans.
Fossil evidence on Terra suggests that all known cetaceans share a common ancestor with land-dwelling mammals that began living in marine environments around 50 million years ago. The Huffh aquired sentience around that time and were transfered to "The Place" by an advanced civilization some time later, creating a permanent divide between the Terran Cetacean and the Huffh. The Cetaceans left on Earth became the mammals best adapted to aquatic life. The body of Terran cetacean is fusiform (spindle-shaped). The forelimbs are modified into flippers. The tiny hindlimbs are vestigial; they do not attach to the backbone and are hidden within the body. The tail has horizontal flukes. Cetaceans are nearly hairless, and are insulated from the cooler water they inhabit by a thick layer of blubber.
While even prior to the Terran Ascent some species were noted for their high intelligence, it was only with the discovery of the Huffh that a naturally evolved sentinent species of Cetacean was confirmed.
For more see the Cetacean article on Wikipedia.