The Collaborative International Dictionary of English v.0.48:

Malacopterygian \Mal`a*cop`ter*yg"i*an\, n. [Cf. F.
   malacopt['e]rygien.] (Zool.)
   One of the Malacopterygii.
   [1913 Webster]

WordNet (r) 3.0 (2006):

malacopterygian
    n 1: any fish of the superorder Malacopterygii [syn: soft-
         finned fish, malacopterygian] [ant: acanthopterygian,
         spiny-finned fish]