Kaksikalvoisia

Kaksikalvoisia is a Finnish term that translates to "bivalve" in English. Bivalves are a class of mollusks, meaning they belong to the phylum Mollusca. This class is characterized by having a shell that consists of two hinged parts, or valves, which are usually symmetrical. These shells are typically composed of calcium carbonate and are secreted by a specialized tissue called the mantle.

Common examples of bivalves include clams, oysters, mussels, and scallops. They are found in a wide variety of aquatic environments, ranging from freshwater rivers and lakes to marine oceans and seas. Many bivalves are filter feeders, using their gills to strain food particles from the water. Others are deposit feeders, consuming organic matter from the seafloor.

The two valves of a bivalve's shell are connected by a flexible ligament, which can be internal or external. Muscles within the shell contract to close the valves, providing protection from predators and environmental conditions. When the muscles relax, the ligament can cause the valves to open, allowing for feeding or movement. Some bivalves can move by extending a muscular foot, while others, like scallops, can swim by rapidly opening and closing their shells to propel themselves through the water. Bivalves play important ecological roles in aquatic ecosystems, including water filtration and as a food source for other animals.