During surveys around the UK, the Eco Marine team have encountered a range of cephalopod species, including the common cuttlefish Sepia officinalis. S. officinalis is the largest cuttlefish species found in the UK and is most often seen around the South of England and Ireland. The body of S. officinalis may grow to 45cm long, with a paired fin running from behind the head along each side of the body. They have two elongated tentacles and eight arms with suckers that are adapted to successfully capture prey.
The terms ‘arm’ and ‘tentacle’ are used to describe two distinct limbs in cephalopod anatomy. Arms have rows of suckers along the entire length of the limb which makes them practical for performing more complex actions or movements. Whereas tentacles are generally longer than the arms and only have suckers near their ends. Tentacles can extend and retract which is beneficial as they are used for prey capture or grasping further away objects.
The word cephalopod is derived from the Greek word ‘kephalopodes’ which literally means “head-feet”. Cephalopods are a class of marine molluscs which includes nautilus, squid, octopus, and cuttlefish. Of the cephalopods, cuttlefish have the largest internal shell, commonly called a ‘cuttlebone’. Squid also possess a narrower, more flexible internal shell commonly termed a ‘pen’. The cuttlebone is an internal structure made of aragonite and it is porous which allows it to aid the animal’s buoyancy. Cuttlebones are often found on beaches across the UK, they appear chalky with an elongated oval shape which is narrower at one end.
S. officinalis live in water up to 200 metres deep but move to shallow waters to breed in spring. In the UK, female cuttlefish typically lay between 200 and 550 eggs in total. The eggs are coated in cuttlefish ink making them appear black and they can take up to 2 months to hatch.
Cuttlefish species are fascinating, in particular due to their impressive ability to camouflage and blend into their surrounding environment. Specialised organs within the skin of cuttlefish called ‘chromatophores’ allow these masters of disguise to mimic the colours of their surroundings or even other fauna, a trait that is useful for avoiding predators. Through the expansion and contraction of sacs of pigment contained within the chromatophores, cuttlefish can bring about the changes in their appearance. Hence the phrase “Chameleons of the sea” being coined to describe them. As well as changing the colour of their skin, cuttlefish can also alter the three-dimensional texture of their skins surface to blend in further with the surrounding environment. Skin texture is controlled by a network of dermal muscles called ‘papillae’.
Many cephalopod species also have this camouflaging ability, including squid and octopus. Cephalopods are highly intelligent animals and their colour changing skin is not used for predator avoidance alone, it is also involved in feeding, mating, and communication. Research on both octopus and cuttlefish has revealed that these cephalopods have the largest brain to body ratio of all invertebrates. Studies on cuttlefish behaviour have revealed they have ‘episodic memory’, which means they can recall previous experiences. This increases cuttlefishes’ ability to learn as they can use memories from previous foraging events to inform and improve future hunting behaviours. The ability to learn from past experiences is a clear sign of intelligence.
Other cephalopods Eco Marine commonly encounter around the UK include the European squid (Loligo vulagris) and the Atlantic Bobtail squid (Sepiola atlantica).
