Mantas and mobulas both belong to the family of devil rays. Their body is wider than long, with a flat head and eyes lying to the side. The large, transverse mouth is surrounded by head fins that are directed forward and guide plankton into the mouth. Mantas grow to about 7 m wide and 5-9 m long (including tail) and have a terminal mouth. The upper side of manta rays has large bright spots on the shoulder and wing tips, the underside is individually spotted. Mobulas are smaller (up to 3 m wide and max. 5 m long) and have an undershot mouth. Mobulas are rather monochrome, dark grey above and without spots below.

Excerpt from "Life in the Red Sea." iBooks.