Shellfish is a culinary term that is often used for several species of molluscs, gastropods, bivalves and arthropods. Some examples are the St. James shell, mussels, razor clams, oysters, cockles and whelks. Most shellfish live partly or fully buried into the seabed, mostly in sandy or gravelly bottoms. They feed by filtering nutrients out of the water. Seed and eggs are released into the water and fertilized externally. Most shellfish are hermaphroditic, they can be both male and female. There are many different shellfish species in the North Sea that are very much suitable for consumption. Fishing methods on shellfish include hand-picking, dredging or mechanic dredges (suckers).
The Ensis genus houses many bivalve species and is also referred to as razor clam or sword razor. Species of the Ensis genus can be found along the entire European coastline. The American jackknife clam is the most common razor clam species which can be found along the Dutch coast. This species is originally found near western Atlantic coastlines but has been introduced in the North Sea via ballast water. Razor clams are bivalves with an oblong, rectangular shell and often live buried in the sand at depths of up to 50 centimetres. Razor clam species usually occur aggregated in large numbers. They also have very well–developed swimming skills; they swim by pushing water out of their shell.