jelly fish

Observation - jelly fish. Description: while swimming with friends at brighton (Rottingdean) we spotted a jelly fish while swimming. i dont have a pictue because i was in the sea swimming. it had a white body and it had brown and spotted tentacles. top to toe was approx about 16cm long and 12

while swimming with friends at brighton (Rottingdean) we spotted a jelly fish while swimming. i dont have a pictue because i was in the sea swimming. it had a white body and it had brown and spotted tentacles. top to toe was approx about 16cm long and 12 and a half cm wide (approx). it looked like a piece of seaweed.we only saw one. can anyone identify it for me.