Red-spotted siphonophore colony. Colonial grouping of red-spotted siphonophores (Forskalia edwardsi), a type of hydrozoa. These marine invertebrates live in colonies made up of a number of highly specialised individual organisms (zooids). The zooids seen here form the nectosome (the propulsion medusae). Each type of zooid (both medusae and polyps) has a specific role to play and none can live without the other. Because of this, siphonophore colonies look like one large organism and can often be mistaken for jellyfish. Photographed in the Mediterranean Sea.