Philip - Octopus

The Octopus by Philip Blackley Phylum Mollusca: The octopus is part of the family Phylum Mollusca and is part of the class Cephalopods. This class of molluscs have the muscular foot in the form of tentacles on their head. Most cephalopods are active predators and eat other living things. They do not have external shells, except the nautilus, and they are the most intelligent of the invertebrates. They all move by jet propulsion. Characteristics: The word octopus is of Greek origin and it means “eight-footed”. It has eight flexible arms, which trail behind it. Most species of octopus have no skeleton and this allows them to squeeze through tight spaces. An octopus has a hard beak with its mouth in the middle of its arms. They are bilaterally symmetrical with two eyes and four sets of limbs, like all other cephalopods. They are very intelligent creatures. In the wild they can build traps and to escape from predators they spit out an inkyblack substance and some can even change colour to blend in with their surroundings such as the Blue-Ringed Octopus. The octopus’s arms are very different to those of a squid. An octopus’s arms are muscular and usually have suction cups on the underside. Octopuses are completely soft which allows them to fit through narrow slits in rocks. This however makes them extremely vulnerable to predators. They have a very short life expectancy, with some of the smaller species surviving for only six months and the larger living for up to five years. The cause of death is reproduction. The males can only live for a few months after mating and the females die shortly after their eggs hatch. They do not eat while taking care of their un-hatched eggs but they do not die of starvation. They are killed by endocrine secretions from the optic glands as a genetically programmed death.

Octopuses have three hearts. Two pump blood through each of the two gills, while the third pumps blood through the body. Octopus blood contains a copper-rich protein hemocyanin which is used to transport oxygen. Although it is less capable under normal conditions than haemoglobin in vertebrates, in cold conditions with low oxygen pressure, hemocyanin is more efficient at transporting oxygen. The hemocyanin is dissolved in the plasma instead of being bound in red blood cells and this gives the blood a blue colour. Octopuses draw water into their mantle cavity where it passes through its gills. Evading Predators: The octopus’s first choice of defence is to hide or not be recognised as an octopus. If it is spotted by a predator it tries fast escape, ink sacs, camouflage and automating limbs. Almost all octopuses can secrete a thick black ink to provide a black cloud to escape. This ink is coloured by melanin which is the same as that which is the same chemical that gives humans their hair and skin colour. The ink is said to have a dull smell which makes it easier to evade sharks, which depend on smell to hunt. Camouflage is created by special skin cells that can change the colour, the opacity and the reflectiveness of the outer skin. These cells can contain yellow, orange, red brown or black pigments. Most species have three of these colours but some can have two or four depending on their surrounding habitat. The colour changing ability can also be used to warn other octopuses. The Great Blue-Ringed octopus turns bright yellow when it feels provoked. Some species of octopus can change the texture of their skin to look like rock of seaweed. This is achieved by the muscles in their arms contracting. Some octopuses can use automating limbs for defence like lizards. They are able to detach an arm and this distracts the attacker. There are also a few species that can imitate dangerous predators like lionfish, eels and sea snakes, such as the Mimic Octopus. Small octopuses can travel with shells that they collect for protection.

Senses and Moving: Octopuses have very good eyesight but they do not have colour vision. This however does not affect them much as they hunt in dark areas. They also have a very good sense of touch. They are able to taste what it is touching through chemoreceptors in the suction cups on their arms. They are able to tell if their arms are stretched out or not but they cannot tell where their arms are. There is a connection between the brain and the arms but it is the nerve cords in the arms that control them, there is no connection however to tell the brain that the arms are doing what it has told them to do. This means that they can only know if they look at their arms visually. Octopuses move about by crawling and swimming. They crawl by walking on their arms and they use this to slowly avoid predators. They swim by jet propulsion. They shoot a jet of water from a contractile mantle and aim using a muscular siphon. The mantle is an important feature of all molluscs and often looks like a cloak or it forms flaps. The siphon is the part of the mantle that water is directed around the body for various uses such as feeding and breathing.