Water covers about three-quarters of the earth and is found in oceans, seas, lakes, streams, ponds, etc. All these bodies of water contain a great variety of flora and fauna. One of those animals that is most easily found in the oceans is the octopus. The octopus is commonly known as the devil fish, as its external appearance is terrible enough to scare a human and other animals. The octopus belongs to the Mollusca phylum and to the Cephalopoda class. The order to which it belongs is Octopoda and its habitat is completely marine.
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 squeeze into small cracks. The power of intelligence is very well developed and it is perhaps the most intelligent animal among all invertebrates. It lives in wide regions of the oceans, but is mainly found among coral reefs. For their defense from enemies, they basically hide or eject an inked 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 lead them to a 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 squid and cuttlefish. They have completely soft bodies with no signs of an exoskeleton like the carapace found in Nautilus and cuttlefish. They have a beak-shaped 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 for only a few months after mating and die later with females dying as soon as the eggs hatch. Females show parental care for their eggs and do not feed until the eggs hatch, but hunger 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 many months after reproduction and, if it later starves, may starve.
There are three hearts in 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 transporter and pigment in your blood. Hemocyanin is a much more efficient oxygen transporter compared to the oxygen transporter hemoglobin of vertebrates. Hemocyanin is dissolved in plasma and is not transported within vertebrate red blood cells and gives blood a blue color. Octopuses draw water from the mantle cavity and, like other mollusks, have finely divided and highly vascularized gills present on the outer or inner surface of the body.
Octopuses are very intelligent and this is a matter of debate among scientists. Experiments have shown that they have short and long-term memory as well. Although they have a very short lifespan, they learn and so far it has not been proven whether young people have innate behaviors or not. They have a very complex nervous system. Two-thirds of neurons are found in the arms, and the arms have remarkable power of autotomy. The arms also show complex reflex actions. Laboratory experiments have shown that they learn to distinguish between shapes and sizes and also to break aquariums in search of food.
The defense mechanism of octopuses basically consists of hiding under any suitable place so that they are not detected by their predators. Another mechanism includes the rapid escape of predators and they also secrete red fluids, show camouflage and break their arms that are also part of their defense mechanism. Most octopuses love to secrete an inked fluid into the water as part of defending their enemies and this inked fluid forms a cloud and confuses the prey and the octopuses run away. This inked fluid consists of a chemical called melanin that is responsible for coloring human skin and hair. The inked fluid reduces the olfactory efficiency of predators and gives octopuses a chance to escape. The chromatophores present in the epidermal layer of the skin of octopuses contain red, yellow, orange and black pigments that make the skin coloration similar to the background and the animal is protected from enemies. The iridophores and leukophores are the reflective cells and are also responsible for the appearance of a 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 as heterocotylus and transfers the spermatophores through it to the cavity of the female’s mantle. In some benthic octopuses, the third arm is the heterocotylus arm. Males generally die after a few months when they have mated. In some species, females store sperm until their eggs have not matured. When the eggs have been fertilized, the females lay around 200,000 eggs and their number varies between species. Females generally attach the eggs in the form of long threads to any solid substrate. Women also show parental care. They protect their eggs from predators and also provide drafts to the eggs so they can get the proper amount of oxygen. Mother octopuses do not hunt and feed until their eggs hatch and they become too weak at that point when their 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 their enemies can easily kill them when they grow old enough to return to the bottom and the cycle repeats.
The sense of vision is very demarcated in octopuses and they can easily distinguish the polarization of light. Color detection is variable between species. The two sense organs of the brain called statocysts help the octopus to detect the orientation of its body. The autonomous response keeps the pupil of the eye horizontal. They have a very good sense of touch. The suction cups present on the arms are generally the chemoreceptors that help the octopus to taste the substance that it is actually touching. The arms also contain strain sensors, so they act as proprioceptors, but researchers need to pay more attention to their actual function. They move by crawling or swimming. They crawl slowly. The 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 of many cultures. The Japanese and Hawaiians are very fond of octopus, as it forms a very important part of their food. They are also used as pets by many people.
Nature has provided a number of special tactics for octopuses to enjoy their life comfortably in their habitat.