a type of jellyfish, specifically from the order Stauromedusae, that remains attached to a substrate by a stalk

comb jellies (Ctenophora)

(zoology) Portuguese man o' war (Physalia physalis)

the free-swimming, bell-shaped stage in the life cycle of a cnidarian, often referred to as a jellyfish

immortal jellyfish (Turritopsis dohrnii)

freshwater jellyfish (genus Craspedacusta)