This is the only pleustonic siphonophore. It has a huge, asymmetric pneumatophore, purplish blue in colour and up to 30 cm in length. The top of the pneumatophore is formed into an erectile "sail" that runs diagonally across it either from the right-hand or left-hand side. The cormidia are attached to one side of the float and their tentacles can stretch down many metres.
Kingdom Animalia Phylum Cnidaria Class Hydrozoa Subclass Siphonophorae Order Cystonectae Family Physaliidae Genus Physalia Species Physalia physalis