Finless Porpoise

The Indo-Pacific finless porpoise is one of eight porpoise species and, as its name says, has no dorsal fin; a ridge studded with small tubercles runs along the back instead. Adults are typically a uniform light grey, sometimes with lighter patches around the mouth or darker patches in front of the flippers. They can reach 2.27 m and 72 kg, although most are smaller, and the flippers are moderately large, up to 20% of body length. Calves of the western subspecies are light creamy grey and darken with age, while calves of the central and eastern subspecies are mostly black and turn grey after four to six months (Wikipedia, general species account).

It lives in the coastal waters of Asia, especially around Indonesia, Malaysia, India and Bangladesh, ranging from the Persian Gulf and the west coast of India to the Indonesian archipelago and north to the Taiwan Strait, where it is replaced northwards by the East Asian finless porpoise. The species is anatomically well studied: its skeleton is unusually light and its hearing is well developed, while its sight is relatively poor (Wikipedia, general species account).