What is "plectognathi"

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

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.