subumbrella

The concave underside of the medusa of a jellyfish or other cnidarian.

The internal ventral or oral disk of a hydrozoan, as a jellyfish; the muscular layer beneath the umbrella or swimming-bell of a hydromedusan, continuous with the velum.

The integument of the under surface of the bell, or disk-shaped body, of a jellyfish.

The integument of the undersurface of the bell, or disk-shaped body, of a jellyfish.