[Amphipoda] Commonly smaller and more delicate than other pereopods, more or less prehensile, and rarely simple. Often the gnathopods are hidden behind other pereopods. The shape of the distal articles of the gnathopod is an important taxonomic character. In gammarids, gnathopods II are usually sexually dimorphic, with the chela or subchela strongly enlarged in males. Such dimorphism is especially noticeable in benthic species, whereas in the planktic ones it is weak, or absent altogether. In hyperiids only genus Phronimopsis has sexually dimorphic gnathopods II, its chela larger in females than in males.

Alternative forms for Gnathopods I and II : Gnathopod I , Gnathopod II, Pereopod I, Pereopod II, Pereopods I and II.