A usually whip-like, multiarticulated appendage of the antennula or the antenna, implanted at the top of the peduncle. The antennula carries two flagella, the antenna one. In most Nephropoidea the antennal flagellum is flexible and whip-like, in most Palinuridae it is rather rigid and may be spinulate. In the Scyllaridae, the flagellum is reduced to a single large plate, which looks as if it were the sixth segment of the antenna. Flagella are also found on some of the exopods of the mouth parts.

Alternative form for flagellum : flagella.