Two of their arms are longer than the other eight and are called tentacles. Squid range in size from under an inch to more than 60 feet in length! They have long, tubular bodies and little heads. Squid are very fast swimmers and use a kind of jet propulsion to move. Squid suck water into a long tube called a siphon and then push it back out.
They can aim the water in any direction. Squid have very good eyesight and may even be able to see in color. The squids' two tentacles are specially adapted for feeding and they use them to grab their prey. They have a sharp beak on their mouths that they use to break open shells.
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Both creatures have similar, though not identical, organ systems. The majority of squid are no more than 60 cm long, although the giant squid may reach 13 m in length. There have even been claims reported of specimens of up to 20 metres 66 ft. Octopuses grow in size from upto 1cm to about 5m. They have a short life span and may not live upto more than 4 to 5 years but can grow quite heavy in weight.
Octopuses and squids move by "jet propulsion", sucking water into a muscular sac in the mantle cavity surrounding their bodies and quickly expelling it out a narrow siphon. Octopuses and squids can swim in any direction and can alter their course quickly.
Squids use fins located on their heads to propel themselves when swimming at low speeds. These fins steer and stabilize the squids when moving slowly, and wrap around the body when they move quickly, by way of jet propulsion. Most octopuses do not have fins as adults. Some deepwater octopuses are exceptions. The eyes of a Squid, found on either side of the head, each contain a hard lens. The lens is focused by moving, much like the lens of a camera or telescope, rather than changing shape like a human eye.
Octopuses use their eight sucker-lined arms to capture their prey and move about on the ocean floor. Squids have eight arms lined with suckers and two specialized tentacles that they use to reach out and capture prey.
Octopuses pierce the shells of their prey, injecting venom that causes paralysis. They then release salivary enzymes, loosening the meat from the inner shell.
Squids use their two specialized tentacles to quickly reach out and capture fishes. They tear off bits of flesh and scrape the meat into their mouths with their beaks.
The male octopus uses a specialized arm called a hectocotylus to transfer sperm to the mantle cavity of a receptive female. The female lays strings of fertilized eggs on the roof of her den. She guards, cleans and aerates the eggs with water expelled from her siphon until hatching—anywhere from 30 days to a year, depending on the species.
The female may build a wall of rocks to seal off the den and will remain in the den until just before she dies, after the eggs have hatched.
Squids often mate in large groups, and attach their egg capsules to the ocean floor or to seaweed. Most adult octopuses and squid die after reproducing. Their bodies are recycled in the food web, nourishing other animals, and ultimately providing food for their young when they hatch. An octopus can camouflage by changing not only its color but also its shape and the texture of its skin.
The following video shows an octopus changing its color and texture while sleeping, leading to the hypothesis that an octopus can probably dream, and is unconsciously reacting to events in a dream. Squids and octopuses are found in salty water from the tropics to the temperate zones.
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