High levels of RNA editing do not appear to be present in more basal cephalopods or other molluscs.  Octopuses are mostly soft tissue, and so fossils are relatively rare. This causes death by respiratory failure leading to cerebral anoxia.  Octopus species that produce larger eggs – including the southern blue-ringed, Caribbean reef, California two-spot, Eledone moschata and deep sea octopuses – do not have a paralarval stage, but hatch as benthic animals similar to the adults. , Nearly all octopuses are predatory; bottom-dwelling octopuses eat mainly crustaceans, polychaete worms, and other molluscs such as whelks and clams; open-ocean octopuses eat mainly prawns, fish and other cephalopods.   An optic gland creates hormones that cause the octopus to mature and age and stimulate gamete production. Other colour-changing cells are reflective iridophores and white leucophores. They are similar in structure to those of a fish and are enclosed in a cartilaginous capsule fused to the cranium. They can extend and contract, twist to left or right, bend at any place in any direction or be held rigid.  The print is a forerunner of tentacle erotica. , When under attack, some octopuses can perform arm autotomy, in a manner similar to the way skinks and other lizards detach their tails. , Most octopuses swim by expelling a jet of water from the mantle through the siphon into the sea. part of "Cirromorphida" (Cirroteuthidae, Stauroteuthidae), part of "Argonautoidea" (Argonautidae, Ocythoidae), part of "Argonautoidea" (Tremoctopodidae, Alloposidae), part of "Cirromorphida" (Opisthoteuthidae, Cirroctopodidae), Octopuses and other coleoid cephalopods are capable of greater RNA editing (which involves changes to the nucleic acid sequence of the primary transcript of RNA molecules) than any other organisms. Hence, greater transcriptome plasticity has come at the cost of slower genome evolution. When resting, around 41% of an octopus's oxygen absorption is through the skin. Ink clouds of some species might act as pseudomorphs, or decoys that the predator attacks instead.  The Octopoda consists of around 300 known species and were historically divided into two suborders, the Incirrina and the Cirrina.  Most of the body is made of soft tissue allowing it to lengthen, contract, and contort itself. , During osmoregulation, fluid is added to the pericardia of the branchial hearts. , The digestive system of the octopus begins with the buccal mass which consists of the mouth with its chitinous beak, the pharynx, radula and salivary glands. He picks up a spermatophore from his spermatophoric sac with the hectocotylus, inserts it into the female's mantle cavity, and deposits it in the correct location for the species, which in the giant Pacific octopus is the opening of the oviduct. , Some robotics research is exploring biomimicry of octopus features. It is not known precisely what contribution learning makes to adult octopus behaviour.  The main pigment in the ink is melanin, which gives it its black colour. The common octopus would be unique for its appearance alone, with its massive bulbous head, large eyes, and eight distinctive arms. A battle with an octopus appears in Victor Hugo's book Toilers of the Sea, inspiring other works such as Ian Fleming's Octopussy. Abdopus aculeatus mostly lives in near-shore seagrass beds.  The mouth of an octopus, located underneath the arms, has a sharp hard beak. The systemic heart is inactive when the animal is swimming and thus it tires quickly and prefers to crawl. , The skin consists of a thin outer epidermis with mucous cells and sensory cells, and a connective tissue dermis consisting largely of collagen fibres and various cells allowing colour change.  When in no hurry, they usually crawl on either solid or soft surfaces.  In colder waters, such as those off of Alaska, it may take as much as 10 months for the eggs to completely develop. It lives in holes or crevices along the rocky bottom and is secretive and retiring by nature.  In addition, the internal shell of incirrates is either present as a pair of stylets or absent altogether. , The octopus is bilaterally symmetrical along its dorso-ventral axis; the head and foot are at one end of an elongated body and function as the anterior (front) of the animal. When it is resting after a meal, absorption through the skin can drop to 3% of its total oxygen uptake. , The reproduction of octopuses has been studied in only a few species. They bite only when provoked or accidentally stepped upon; bites are small and usually painless. Updates? Octopuses vary greatly in size: the smallest, O. arborescens, is about 5 cm (2 inches) long, while the largest species may grow to 5.4 metres (18 feet) in length and have an arm span of almost 9 metres (30 feet). ( See cephalopod .) The molecular analysis of the octopods shows that the suborder Cirrina (Cirromorphida) and the superfamily Argonautoidea are paraphyletic and are broken up; these names are shown in quotation marks and italics on the cladogram. Upon hatching, the tiny octopods, which closely resemble their parents, spend several weeks drifting in the plankton before taking refuge on the bottom.  A study of this behaviour led to the suggestion that the two rearmost appendages may be more accurately termed "legs" rather than "arms".  Although several species are known to live at bathyal and abyssal depths, there is only a single indisputable record of an octopus in the hadal zone; a species of Grimpoteuthis (dumbo octopus) photographed at 6,957 m (22,825 ft). Strategies to defend themselves against predators include the expulsion of ink, the use of camouflage and threat displays, the ability to jet quickly through the water and hide, and even deceit. This moves the body slowly.  An octopus may spend 40% of its time hidden away in its den. Basal species, the Cirrina, have stout gelatinous bodies with webbing that reaches near the tip of their arms, and two large fins above the eyes, supported by an internal shell. The gonocoel is connected by the gonoduct to the mantle cavity, which it enters at the gonopore.  Water flow over the gills correlates with locomotion, and an octopus can propel its body when it expels water out of its siphon.  Bites have been recorded from captive octopuses of other species; they leave swellings which disappear in a day or two.  Octopuses hide in dens, which are typically crevices in rocky outcrops or other hard structures, though some species burrow into sand or mud. As progress is made, other arms move ahead to repeat these actions and the original suckers detach. , Octopuses are gonochoric and have a single, posteriorly-located gonad which is associated with the coelom.  However, more recent evidence suggests that Cirrina are merely the most basal species and are not a unique clade.  In 2017 a German company made an arm with a soft pneumatically controlled silicone gripper fitted with two rows of suckers. (See cephalopod.).  Cirrate octopuses lack the ink sac. In the UK from 1993 to 2012, the common octopus (Octopus vulgaris) was the only invertebrate protected under the Animals (Scientific Procedures) Act 1986.  This form of locomotion allows these octopuses to move quickly away from a potential predator without being recognised. The octopus carries the shells underneath it with two arms, and progresses with an ungainly gait supported by its remaining arms held rigid. :276–277 Experimental removal of both optic glands after spawning was found to result in the cessation of broodiness, the resumption of feeding, increased growth, and greatly extended lifespans. Octopuses appear in mythology as sea monsters like the Kraken of Norway and the Akkorokamui of the Ainu, and probably the Gorgon of ancient Greece. , Due to their intelligence, octopuses are listed in some countries as experimental animals on which surgery may not be performed without anesthesia, a protection usually extended only to vertebrates. Octopus arms can move and sense largely autonomously without intervention from the animal's central nervous system. When a sucker attaches to a surface, the orifice between the two structures is sealed. The ingress of water is achieved by contraction of radial muscles in the mantle wall, and flapper valves shut when strong circular muscles force the water out through the siphon. Octopuses that are diurnal and live in shallow water have evolved more complex skin than their nocturnal and deep-sea counterparts.
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