3 euro – Blue-ringed octopus

The blue-ringed octopus is a brilliant example of how fascinating and colourful the underwater world can be. One of the most intelligent invertebrates, this amazing animal is not only smart but also highly toxic. If it feels threatened its rings illuminate several times per second. This is exactly what it does on the first coin in the Luminous Marine Life series. You will be amazed. Many octopuses can change their skin colour and even their body shape in a flash. Special cells in the skin contain pigments with different colour properties, some of which only reflect light in certain colours when it shines on them. This property is known as ‘iridescence’, which means that different colours appear on a surface depending on the angle of view. Muscle tension can cause these pigments to contract or expand and so the blue-ringed octopus can change the colour of its skin in certain places. Another amazing thing about the octopus is that it not only has a central brain in its head, but also has other brains in its eight tentacles. This enables octopuses to always have everything under control and to adapt very quickly to their environment. This is why octopuses are considered the smartest invertebrates. Although one of the world’s most venomous marine animals, the blue-ringed octopus can be encountered on bathing beaches in the Pacific and Indian Oceans and therefore comes into contact with humans on a regular basis. The octopus signals its presence with the rapid flashing of its blue rings and is only dangerous to humans if it bites them, which only occurs if it feels very threatened.