I think the food capture by the mucus method takes place on the surface of the bell, rather than the "undersides". It might be also interesting to point out that the mouth is also the anus. Disambiguation with ctenophores ("snot pets" or "comb jellies") that have the brilliant advancement of a mouth separate from the anus might also be interesting. Both tend to wash up as little gelatinous mounds. People tend to be afraid of both, but moon jellies don't usually cause a sting for most people and ctenophores don't sting.