The Collaborative International Dictionary of English v.0.48:

Plectognathi \Plec*to"gna*thi\, n. pl. [NL., from Gr. ? twisted
   (fr. ? to plait, twist) + ? jaw.] (Zool.)
   An order of fishes generally having the maxillary bone united
   with the premaxillary, and the articular united with the
   dentary.
   [1913 Webster]

   Note: The upper jaw is immovably joined to the skull; the
         ventral fins are rudimentary or wanting; and the body
         is covered with bony plates, spines, or small rough
         ossicles, like shagreen. The order includes the
         diodons, filefishes, globefishes, and trunkfishes.
         [1913 Webster] Plectognathic

WordNet (r) 3.0 (2006):

Plectognathi
    n 1: boxfishes; filefishes; globefishes; ocean sunfishes;
         triggerfishes; puffers [syn: Plectognathi, order
         Plectognathi, order Tetraodontiformes]