The blue whale's body is long and slender. It can be various shades of bluish-grey above and somewhat lighter underneath. There are at least three different subspecies: "B. m. musculus" of the North Atlantic and North Pacific, "B. m. intermedia" of the Southern Ocean and "B. m. brevicauda" (also known as the pygmy blue whale) found in the Indian Ocean and South Pacific Ocean. "B. m. indica", found in the Indian Ocean, may be another subspecies. As with other baleen whales, its diet consists almost exclusively of small krill.