Amphipoda \Am*phip"o*da\, n. pl. [NL., FR. Gr. ? + ?, ? foot.]

(Zo["o]l.) A numerous group of fourteen -- footed Crustacea, inhabiting both fresh and salt water. The body is usually compressed laterally, and the anterior pairs or legs are directed downward and forward, but the posterior legs are usually turned upward and backward. The beach flea is an example. See Tetradecapoda and Arthrostraca.

Source: Webster's Revised Unabridged Dictionary (1913)