There are about 375 species of squid. Squid have 10 arms. 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.
Squid have some unique adaptations. Some can change color, some use bioluminescence to create light, and some shoot ink to cloud the water and lose predators. Squid usually travel in groups and can be found in the sunlit zone and the twilight zone.
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Technically, oysters don't have very many adaptations. Oysters are very good at resisting heat and they can also camouflage with other shells or organisms. Also, they are creatures that don't move very often so they can filter feed instead of going out into the ocean with other predators on the loose.
Oysters breathe much like fish, using both gills and mantle. The mantle is lined with many small, thin-walled blood vessels which extract oxygen from the water and expel carbon dioxide. A small, three-chambered heart, lying under the adductor muscle, pumps colorless blood, with its supply of oxygen, to all parts of the body. At the same time a pair of kidneys located on the underside of the muscle purify the blood of any waste products it has collected.
While oysters have separate sexes, they may change sex one or more times during their life span. The gonads, organs responsible for producing both eggs and sperm, surround the digestive organs and are made up of sex cells, branching tubules and connective tissue.
