There are about 42 species of dolphins, in which 32 are oceanic dolphins, 4 are river dolphins and 6 are porpoises. Often it is hard to distinguish between porpoises and dolphins, but porpoises have a relatively short snout and round faces while dolphins have long snout or beak. The orcas or killer whales are actually the largest dolphins and their size is normally up to 9.5m (30 feet) and weight is about 10 tons.