The margin of the bell has sixteen lappets (folds), the niches between these bearing alternately rhopalia (sense organs) and short tentacles (eight of each).

[1][5] The thimble jellyfish is found in the tropical and subtropical western Atlantic Ocean, particularly around the West Indies and the Bahamas.

When edible zooplankton are encountered, they are immobilised by the cnidocytes (stinging cells) and passed by the tentacles to the mouth on the underside of the bell.

When the swimmer exits the water and either bathes or drys out, the larvae are killed and in the process discharge their under-developed stinging cells.

A similar condition occurs on the west coast of North America after exposure to the larvae of the sea anemone Edwardsiella lineata.