The rhizostome is a planktonic jellyfish, which moves slowly in shallow water (gelatinous macroplankton, necton) and which generally abounds in the coastal environment. It is common in lagoons and estuaries.
Also called cauliflower jellyfish (Rhizostoma pulmo - syn Rhisostoma octopus), its parasol is ball-shaped and can reach 1 meter in diameter. Light blue in color, its parasol is bordered by a dark blue border. It does not have tentacles but four mouth arms divided in two. We meet it from August to November.
Rhizostoma octopus
Dangerousness
This jellyfish, despite its impressive size, is in principle harmless because it no longer has tentacles. However, in some more sensitive people, skin irritation reactions (redness, itching) have been reported. Sometimes people experience burns without direct contact with the jellyfish, but the jellyfish was jostled and stinging mucus could reach the bodies of individuals nearby.