The Collaborative International Dictionary of English v.0.48:

manta ray \manta ray\ n.
   An extremely large pelagic tropical ray of the family
   Mobulidae, that feeds on plankton and small fishes. It is
   usually harmless but its size (up to 20 feet across and up to
   a ton in weight) make it dangerous if harpooned. Called also
   manta, sea devil and devilfish. See also Cephaloptera
   and Sea devil.
   [WordNet 1.5 +PJC]

The Collaborative International Dictionary of English v.0.48:

Cephaloptera \Ceph`a*lop"te*ra\
   (s[e^]f`[.a]*l[o^]p"t[-e]*r[.a]), n. [NL., fr. Gr. kefalh`
   head + ptero`n wing.] (Zool.)
   One of the generic names of the gigantic ray (Manta
   birostris) of the family Mobulidae, known as devilfish,
   sea devil, manta and manta ray. It is common on the
   coasts of South Carolina, Florida, and farther south, and is
   sometimes found as far north as New York Bay. Some of them
   grow to enormous size, becoming twenty feet of more across
   the body, and weighing more than a ton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

manta ray
    n 1: extremely large pelagic tropical ray that feeds on plankton
         and small fishes; usually harmless but its size make it
         dangerous if harpooned [syn: manta, manta ray,
         devilfish]