Sepia sewelli is a species of cuttlefish native to the western Indian Ocean, from Cape Guardafui, Somalia (11°57′N 50°35′E / 11.950°N 50.583°E / 11.950; 50.583 to 05°40′S 39°17′E / 5.667°S 39.283°E / -5.667; 39.283) to Zanzibar and probably Madagascar. It lives at depths of 37 to 238 m.
Sepia sewelli grows to a mantle length of 30 mm.
The type specimen was collected near Cape Guardafui (11°57′12″N 50°35′00″E / 11.95333°N 50.58333°E / 11.95333; 50.58333 to 11°56′42″N 50°39′12″E / 11.94500°N 50.65333°E / 11.94500; 50.65333) and is deposited at The Natural History Museum in London.
