Thousands of incredibly beautiful blue button “jellyfish” filled our lagoon recently, creating what looked like an enormous bath of blue flowers in the turquoise water.
These blue buttons are not jellyfish at all, and thankfully they do not sting!
Blue buttons are actually what we call hydrozoans which belong to the same animal phylum as the jellyfish - Cnidaria. They are closely related to the “true” jellyfish, box jellyfish, sea anemones and corals and share with them the group’s distinct feature: specialized cells that carry stinging organelles. The blue button (Porpita porpita) however is harmless to humans as the stinging cells are unable to pierce the skin.
Although related to jellyfish, blue buttons are in fact colonial animals that are characterised by the cooperative action of small polyps with different functions; some are responsible for defence, some for feeding, others for reproduction etc. These pelagic colonies cannot actively move/swim but drift on the surface of the open sea, partially using a central disc-shaped float made up of numerous chambers and blue or green tentacles that are used for feeding on microscopic organisms near the water surface. Their colour is usually a dark blue, which is thought to help avoid predation by birds.
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