Octopus | Fish | Octopuses are mollusks from the cephalopod ("cephalopod": feet located in the head), the order Octopoda with coral reefs in the ocean as the main habitat. Octopus consists of 289 species that includes a third of the total cephalopod species in the world. Octopuses are any cephalopods (class Cephalopoda, phylum Mollusca) belonging to the order Octopoda. An octopus is characterized by having eight arms and simple suckers without secondary armature (O'Shea, 2006). The term octopus (Greek: Ὀκτάπους, eight legs) may also refer to only those creatures in the genus Octopus.
Like all cephalopods, octopuses have bilateral symmetry, a prominent head, and a modification of the mollusk foot into the form of arms or tentacles surrounding the mouth, which has beak-like jaws.
Octopuses belong to the subclass Coleoidea along with squids, cuttlefish, and extinct belemites. They differ from squids and the squid-like cuttlefish because squids and cuttlefish at some point in their life cycle have eight arms and two tentacles, whereas octopuses have eight arms and no tentacles. (Tentacles tend to be longer than arms and usually have suckers as their tips only.) Furthermore, while octopuses are characterized by simple suckers, the suckers of squids also are armed by hooks or sucker rings (O'Shea 2006). Some squid species lose their tentacles in post-larval stages, and thus the adult only has eight arms like the octopus (O'Shea, 2006).
Octopuses not only contribute to the food chains in ocean environments, but contribute many values to humans, including as a food delicacy, and as creatures whose intelligence, movements, camouflage, beauty, power, and defense and predatory techniques have fascinated human beings for thousands of years.
All cephalopods are marine organisms. Octopuses inhabit many diverse regions of the ocean, especially coral reefs. In the larger sense of the term, there are about 300 different octopus species, which is over one-third of the total number of cephalopod species.
Octopuses are characterized by their eight arms (not tentacles), usually bearing suction cups. These arms are a type of muscular hydrostat.
Unlike most other cephalopods, the majority of octopuses—those in the suborder most commonly known (Incirrata)—have almost entirely soft bodies with no internal skeleton. They have neither a protective outer shell like the nautilus, nor any vestige of an internal shell or bones, like cuttlefish or squids. A beak, similar in shape to a parrot's beak, is their only hard part. This enables them to squeeze through very narrow slits between underwater rocks, which is very helpful when they are fleeing from moray eels or other predatory fish. The octopuses in the less familiar Cirrata suborder have two fins and an internal shell, generally lessening their ability to squeeze into small spaces.
|Blue ringed octopus|
Octopuses have a relatively short life span, and some species live for as little as six months. Larger species, such as the North Pacific Giant Octopus, may live for up to five years under suitable circumstances. However, reproduction is a cause of death: males can only live for a few months after mating, and females die shortly after their eggs hatch, for they neglect to eat during the roughly one-month period spent taking care of their unhatched eggs.
Octopus has three hearts. Gill, two hearts to pump blood through the two gills, while the third pumps blood through the body. Octopus blood contains the copper-rich protein hemocyanin to carry oxygen. Less efficient than the iron-rich hemoglobin of vertebrates, hemocyanin is dissolved in blood plasma, instead of being tied to red blood cells and gives a blue color. Octopus pulls water from the mantle cavity where it passes through the gills. As mollusks, octopuses have gills that are finely divided and vascularized outgrowths or external or internal body surface. - FISH
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