Like many cephalopods, the mimic octopus (Thaumoctopus mimicus) has the ability to change the colour of its skin. However this species goes a step further and, as its name suggests, is able to accurately imitate up to 13 other animals present in its habitat. It typically has cream or white and dark brown bands and grows to have a maximum arm span of 60cm. It was discovered in the Indo-Pacific Ocean in 1998 and over the last few years has become known as a remarkable artist of disguise.
The mimic octopus is a sand and silt dwelling cephalopod that is found at depths of between 2 and 12 meters, close to river mouths in a habitat where the seabed is rich in fauna such as crustaceans and worms, which the octopus feeds upon. It is able to quickly alter its appearance and behaviour to camouflage itself, or scare potential predators by seemingly imitating potentially dangerous or venomous creatures. For example, to avoid attack from a territorial fish such as a damselfish, the octopus appears to mimic a banded sea snake which is poisonous and preys on small fish, like the damselfish. To achieve this, the octopus hides 6 of its arms behind its body in a hole and raises the remaining two arms in opposite directions, moving them in an undulating, curling fashion to imitate the movements of a snake. The intelligence of the mimic octopus is demonstrated by its remarkable ability to choose the species it mimics depending on the type of predator that it is threatening it.
It is active during the daylight hours, which is fine for relatively stationary activities such as foraging as it can alter its skin colour and camouflage itself, however it poses the problem of moving between sites where it wishes to forage for food while maintaining camouflage to protect itself from predators. A solution to this is achieved by appearing to adopt the colouring, shape and style of movement of a common flatfish. The octopus has been seen on several occasions swimming between foraging sites such as worm holes in this way. To achieve this, the mimic octopus takes on the streamlined, leaf-like shape of the flatfish by trailing all its arms behind itself and by taking on the colouring of a specific species of sole that is found in the same habitat as the mimic octopus. This particular sole (Zebrias spp.) is very well camouflaged and moves quickly, undulating and hugging the sea bed. It also possesses two poison glands, thus making it unattractive to predators.
The mimic octopus’s apparent imitation of the lion fish is another example of its ability to take on the appearance of other organisms in order to move safely though open water as, due to its poison, most predators do not attack the lionfish. Although it is a predominantly benthic organism that lives and feeds on the sea bed, the mimic octopus is able to swim along a little above the sea –floor with its arms matching the colouring of the lionfish and trailing behind it, like the lionfish’s poison tipped spines.
It is specialised cells in the skin of the octopus that reflect, absorb, diffract and scatter light in different ways and so create the colour changing ability of the mimic octopus which makes the majority of the different appearances it is able to assume possible. There are 4 different types of cell that facilitate colour change, the main type being chromatophores.
Chromatophores are found directly under the surface of the skin of cephalopods. These are groups of cells that include a pigment contained in a saccule and a group of muscles that, when they contract, expand the saccule and make more of the pigment visible. The pigment contained in the saccule can be yellow, orange, red, brown or black in colour. Each chromatophore is attached to a nerve ending so when a trigger is sent from the brain the amount of visible pigment can be altered very rapidly across many chromatophores and a pattern produced.
Although chromatophores are the main colour change organs, the other colour changing cells types that are important too. A layer of skin below the chromatophores are the iridophores. These create the more metallic looking colours such as gold, green, blue and occasionally silver. These are not as easy to control as the chromatophores as they are not neurally controlled, but controlled by hormones. Another type of cells causing colouring in cephlopods are the leucophores that reflect and scatter light, meaning that they appear to be different colours depending on the predominant wavelength of the light of the area.
There is still much to discover about the mimic octopus as it is relatively new to science and, despite the popularity of this creature, there has been little research into it. This means that there is still a long way to go before we fully understand its intelligence and hopefully in the future we will be able to find out more about this amazing and bizarre creature.
Dynamic mimicry in an Indo-Malayan octopus, 2005, MARK D. NORMAN, JULIAN FINN AND TOM TREGENZA
Chromatophore Organs, Reflector Cells, Iridocytes and
Leucophores in Cephalopods, 1983, RICHARD A. CLONEY AND STEVEN L. BROCCO
Mimicry and foraging behaviour of two tropical sand-flat octopus species off North Sulawesi, Indonesia, 2008, ROGER T. HANLON, LOU-ANNE CONROY and JOHN W. FORSYTHE
The evolution of conspicuous facultative mimicry in octopuses: an example of secondary adaptation?, 2010, CHRISTINE L. HUFFARD, NORAH SAARMAN, HEALY HAMILTON and W. BRIAN SIMISON