instruction: How big is Reef manta rays
context: The reef manta ray (Mobula alfredi) is a species of ray in the family Mobulidae, one of the largest rays in the world. Among generally recognized species, it is the second-largest species of ray, only surpassed by the giant oceanic manta ray.
  
  The species was described in 1868 by Gerard Krefft, the director of the Australian Museum. He named it M. alfredi in honor of Alfred, Duke of Edinburgh, the first member of the British royal family to visit Australia. It was originally described as part of the genus Manta but in 2017 was changed, along with the rest of the mantas, to be included as part of the genus Mobula.
  
  Reef manta rays are typically 3 to 3.5 m (9.8 to 11.5 ft) in disc width, with a maximum size of about 5.5 m (18 ft). For a long time included in M. birostris, the status of the reef manta ray as a separate species was only confirmed in 2009. The reef manta ray is found widely in the tropical and subtropical Indo-Pacific, but with a few records from the tropical East Atlantic and none from the West Atlantic or East Pacific. Compared to the giant oceanic manta ray, the reef manta ray tends to be found in shallower, more coastal habitats, but local migrations are sometimes reported. Mobula birostris is similar in appearance to Mobula alfredi and the two species may be confused as their distribution overlaps. However, there are distinguishing features.
response: Reef manta rays are typically 3 to 3.5 m (9.8 to 11.5 ft) in disc width, with a maximum size of about 5.5 m (18 ft).