When the tide goes out, it leaves behind areas of standing water known as rock pools. A wide variety of animals live in these pools, using the water available to ensure that their gills stay wet and they maintain their ability to breathe. These animals have evolved traits that allow them to retain water during low tide.
Mollusks are a large group of organisms that include limpets, chitons and whelks. They have soft, unsegmented bodies, muscular feet or tentacles, and an organ called a radula that they use to grasp rock surfaces or, in some cases, to cut up prey. The teeth on chitons, for example, are so hard that they can grind through rock.
Classified as animals, sponges draw water into a cavity in which food particles are then contained and digested. The most common sponges found in rock pools are of the encrusting variety, which are typically found in the low-tide area where they attach themselves to rock surfaces.
Arthropods are a group of animals characterised by an external skeleton that they shed and regrow as they mature. Arthropods include such well-known animals as crabs, shrimp, lobsters and barnacles. These animals live inside shells and use their legs to filter out food. During low tide they have the ability to close their shells to ensure that they do not dry out.
Although most people associate worms with the soil, several species also make their home in rock pools. The most common variety are the tube worms, which only come out of their shells when the high tide comes in, at which time they use their tentacles to obtain food particles. Other varieties of worms also have a nose that they use to eat food.
Despite the fact that they resemble flowers, sea anemones are animals that devour their prey after trapping it. The most common variety found in the rock pool environment is the sand anemone, which uses a variety of materials, including sand, gravel, and bits of shell, to camouflage itself.