The lion’s mane jelly tentacles (Cyanea capillata) can extend 30 feet (9m) into the water!  These long tentacles are often difficult for a diver to see and can deliver a nasty sting.  I remember a dive where someone had a tentacle drag across their exposed upper lip.  After the dive his lip looked very swollen and he was driven to the hospital.  If stung, apparently meat tenderizer or vinegar is a good antidote.  Although as a diver it’s good to be careful around the lion’s mane jelly, it is very interesting to observe one up close.  This pelagic jelly has a west coast range from northern Alaska to southern California.