: an annular membrane projecting inward from the margin of the bell in some jellyfishes (such as the hydromedusae)
2
: a swimming organ that is especially well developed in the later larval stages of many marine gastropods
Word History
Etymology
borrowed from Latin vēlum "awning, curtain"; in sense 1a short for New Latin vēlum palātī or vēlum palātīnum, literally, "curtain of the palate" — more at veil entry 1