Water covers approximately three quarters of the earth and is found in oceans, seas, lakes, streams, ponds, etc. All these bodies of water contain a wide variety of flora and fauna. One such animal that is most easily found in the oceans is the octopus. The octopus is commonly known as the devil fish, since its external appearance is terrifying enough to scare a human and other animals. The octopus belongs to the phylum Mollusca and class Cephalopoda. The order to which it belongs is Octopoda and it has a completely marine habitat.

The octopus has two eyes and four pairs of arms and, like other cephalopods, its body is bilaterally symmetrical. It has a beak and the mouth is located in the central position of the arms. The exoskeleton is absent, so it can get into small crevices. The power of intelligence is very well developed and it is perhaps the most intelligent animal among all invertebrates. It inhabits wide regions of the oceans, but is found mainly among coral reefs. For their defense from enemies they basically hide or eject an ink material or display a color changing activity called camouflage. All octopuses are generally poisonous, but only the small blue-ringed octopuses are harmful to humans and take them to the heavenly abode. Currently about 300 species of octopus are known.

Octopuses are very clearly identified by their eight dangerous arms, each with suction cups. Their arms are very different from those found in other cephalopods such as squids and cuttlefish. They have completely soft bodies with no signs of an exoskeleton like the shell found in Nautilus and cuttlefish. They have a beak-like structure similar to that of a parrot but very small in size and it is the only hard structure present on their bodies. Their soft bodies allow them to hide under small areas when attacked. They have a very short lifespan, but some species can live up to six months. The giant North Pacific octopus can live up to five years under certain conditions. Their life expectancy is basically affected by reproduction. Males live only a few months after mating and die later and females die as soon as the eggs hatch. Females show parental care for their eggs and do not feed until they hatch, but starvation is not the cause of their death. The two optic glands secrete endocrine substances that are responsible for programmed cell death. It has been found that if these optic glands are surgically removed, the octopus survives for many months after breeding, and if it then starves, it may die of starvation.

There are three hearts on the octopuses. The two are responsible for pumping blood from the two gills and the third is responsible for pumping blood throughout the body. Your blood carries a copper-containing protein hemocyanin, which is the oxygen carrier and blood pigment. Hemocyanin is a much more efficient oxygen carrier compared to the oxygen-carrying hemoglobin of vertebrates. Hemocyanin is found dissolved in plasma and is not transported within the red blood cells of vertebrates and gives blood a blue color. Octopuses draw water from their mantle cavity and, like other mollusks, have highly vascularized, finely divided gills present on the external or internal surface of the body.

Octopuses are very intelligent and this is a matter of debate among scientists. Experiments have shown that they have short-term and long-term memory as well. Although they have a very short lifespan, they do learn, and whether or not the young have innate behaviors has not been shown so far. They have a very complex nervous system. Two-thirds of the neurons are located in the arms, and the arms have remarkable autotomy powers. The arms also show complex reflex actions. Laboratory experiments have shown that they learn to distinguish between shapes and sizes and also break out of aquariums in search of food.

The defense mechanism of octopuses basically consists of hiding under any suitable place so as not to be detected by its predators. Other mechanism includes rapid escape from predators and they also secrete ink fluids, display camouflage, and break their arms, which is also part of their defense mechanism. Most of the octopuses love to secrete an ink fluid into the water as part of their defense from their enemies and this ink fluid forms a cloud and confuses the prey and the octopuses run away. This ink liquid consists of a chemical called melanin which is responsible for giving human skin and hair its color. The ink liquid reduces the predators’ olfaction efficiency and gives the octopuses a chance to escape. The chromatophores present in the epidermal layer of the octopus skin contain red, yellow, orange and black pigments that make the skin color similar to the background and the animal is protected from enemies. Iridophores and leucophores are the reflective cells and are also responsible for the appearance of warning coloration. They also break their arms when attacked and their broken arms regenerate later.

The act of reproduction in octopuses is very different. During the act of reproduction, the male uses his special arm designated the heterocotylus and transfers the spermatophores through it into the mantle cavity of the female. In some benthic octopuses, the third arm is the heterocotylus arm. The males usually die after a few months when they have mated. In some species, females store sperm until their eggs have matured. When the eggs have been fertilized, the females lay around 200,000 eggs, the number of which varies between species. Females generally attach the eggs in the form of long strings to any solid substrate. Females also show parental care. They protect their eggs from predators and also provide air currents to the eggs so they can get the proper amount of oxygen. Mother octopuses do not hunt and do not feed until the eggs hatch and become too weak at that time when the eggs hatch and can be easily killed by predators. The young larvae that hatch from the eggs move to the upper surface of the sea and feed on plankton like copepods. This timing is very critical as they can be easily killed by their enemies when they grow large enough to go back to the bottom and the cycle repeats.

The sense of vision is very limited in octopuses and they can easily distinguish the polarization of light. Color detection is variable between species. The two sensory organs in the brain called statocysts help the octopus detect the orientation of its body. The autonomic response maintains the pupil of the eye in a horizontal position. They have a very good sense of touch. The suckers present on the arms are generally the chemoreceptors that help the octopus taste the substance it is touching. The arms also contain strain sensors, so they act as their own receptors, but their actual function needs more attention from researchers. They move by crawling or swimming. They creep slowly. Jet propulsion performed by them is their fastest mode of locomotion, followed by swimming and crawling. Octopuses were worshiped by ancient people. They are often eaten as food by humans from many cultures. The Japanese and Hawaiians are very fond of octopus as it forms a very important part of their diet. They are also used as pets by many people.

Nature has provided the octopus with a series of special tactics to enjoy its life comfortably in its habitat.