Burgessomedusa is an extinct, monotypic genus of macroscopic free-swimming cnidarians from the middle Cambrian Burgess Shale in Canada. The type species is Burgessomedusa phasmiformis. The genus was characterized by the bell-like body with about 90 short tentacles. They led a predatory lifestyle and reached a length of 20 cm. It is considered as the oldest unambiguous free-swimming medusa, if potential older records from other fossil sites represent ctenophores instead.

Jellyfish, also known as sea jellies, are the medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria.