Oyster in the context of "Filter feeder"

Clam is a common name for several species of bivalve mollusc. The word is often applied only to those that are deemed edible and live as infauna, spending most of their lives halfway buried in the sand of the sea floor or riverbeds. Clams have two shells of equal size connected by two adductor muscles and have a powerful burrowing foot. They live in both freshwater and marine environments; in salt water they prefer to burrow down into the mud and the turbidity of the water required varies with species and location; the greatest diversity of these is in North America.

Clams in the culinary sense do not live attached to a substrate (whereas oysters and mussels do) and do not live near the bottom (whereas scallops do). In culinary usage, clams are commonly eaten marine bivalves, as in clam digging and the resulting soup, clam chowder. Many edible clams such as palourde clams are ovoid or triangular; however, razor clams have an elongated parallel-sided shell, suggesting an old-fashioned straight razor.

Shellfish, in colloquial and fisheries usage, are exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environments, some are found in freshwater. In addition, a few species of land crabs are eaten, for example Cardisoma guanhumi in the Caribbean. Shellfish are among the most common food allergens.

Due to narrowing in the meaning of the English word fish over the centuries, shellfish no longer fall under what is usually considered fish. Most shellfish are low on the food chain and eat a diet composed primarily of phytoplankton and zooplankton. Many varieties of shellfish, and crustaceans in particular, are actually closely related to insects and arachnids; crustaceans make up one of the main subphyla of the phylum Arthropoda. Molluscs include cephalopods (squids, octopuses, cuttlefish) and bivalves (clams, oysters), as well as gastropods (aquatic species such as whelks and winkles; land species such as snails and slugs).

Seafood is any form of sea life regarded as food by humans, prominently including fish and shellfish. Shellfish include various species of molluscs (e.g., bivalve molluscs such as clams, oysters, and mussels, and cephalopods such as octopus and squid), crustaceans (e.g. shrimp, crabs, and lobster), and echinoderms (e.g. sea cucumbers and sea urchins). Historically, marine mammals such as cetaceans (whales and dolphins) as well as seals have been eaten as food, though that happens to a lesser extent in modern times. Edible sea plants such as some seaweeds and microalgae are widely eaten as sea vegetables around the world, especially in Asia.

Seafood is an important source of (animal) protein in many diets around the world, especially in coastal areas. Semi-vegetarians who consume seafood as the only source of meat are said to adhere to pescetarianism.

Pearl hunting, also known as pearl fishing or pearling, is the activity of recovering or attempting to recover pearls from wild molluscs, usually oysters or mussels, in the sea or freshwater. Pearl hunting was prevalent in India and Japan for thousands of years. On the northern and north-western coast of Western Australia pearl diving began in the 1850s, and started in the Torres Strait Islands in the 1860s, where the term also covers diving for nacre or mother of pearl found in what were known as pearl shells.

In most cases the pearl-bearing molluscs live at depths where they are not manually accessible from the surface, and diving or the use of some form of tool is needed to reach them. Historically the molluscs were retrieved by freediving, a technique where the diver descends to the bottom, collects what they can, and surfaces on a single breath. The diving mask improved the ability of the diver to see while underwater. When the surface-supplied diving helmet became available for underwater work, it was also applied to the task of pearl hunting, and the associated activity of collecting pearl shell as a raw material for the manufacture of buttons, inlays and other decorative work. The surface supplied diving helmet greatly extended the time the diver could stay at depth, and introduced the previously unfamiliar hazards of barotrauma of ascent and decompression sickness.

Spontaneous generation is a superseded scientific theory that held that living creatures could arise from non-living matter and that such processes were commonplace and regular. It was hypothesized that certain forms, such as fleas, could arise from inanimate matter such as dust, or that maggots could arise from dead flesh. The doctrine of spontaneous generation was coherently synthesized by the Greek philosopher and naturalist Aristotle, who compiled and expanded the work of earlier natural philosophers and the various ancient explanations for the appearance of organisms. Spontaneous generation was taken as scientific fact for two millennia. Though challenged in the 17th and 18th centuries by the experiments of the Italian biologists Francesco Redi and Lazzaro Spallanzani, it was not discredited until the work of the French chemist Louis Pasteur and the Irish physicist John Tyndall in the mid-19th century.

Among biologists, rejecting spontaneous genesis is no longer controversial. Experiments conducted by Pasteur and others were thought to have refuted the conventional notion of spontaneous generation by the mid-1800s. Since all life appears to have evolved from a single form approximately four billion years ago, attention has instead turned to the origin of life.

Gryphaea, one of the genera known as devil's toenails, is a genus of extinct oysters, marine bivalve mollusks in the family Gryphaeidae.

These fossils range from the Triassic period to the middle Paleogene period, but are mostly restricted to the Triassic and Jurassic. They are particularly common in many parts of Britain.

A seashell (or sea shell), also known simply as a shell, is a hard, protective outer layer usually created by an animal or organism that lives in the sea. Most seashells are made by mollusks, such as snails, clams, and oysters to protect their soft insides. Empty seashells are often found washed up on beaches by beachcombers. The shells are empty because the animal has died and the soft parts have decomposed or been eaten by another organism.

A seashell is usually the exoskeleton of an invertebrate (an animal without a backbone), and is typically composed of calcium carbonate or chitin. Most shells that are found on beaches are the shells of marine mollusks, partly because these shells are usually made of calcium carbonate, and endure better than shells made of chitin.

Bivalvia (/baɪˈvælviə/) or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consisting of a hinged pair of half-shells known as valves. As a group, bivalves have no head and lack some typical molluscan organs such as the radula and the odontophore. Their gills have evolved into ctenidia, specialised organs for feeding and breathing.

Common bivalves include clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. Majority of the class are benthic filter feeders that bury themselves in sediment, where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as scallops and file shells, can swim. Shipworms bore into wood, clay, or stone and live inside these substances.