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At first sight, these animals resemble molluscs somewhat. Like a mussel, a brachiopod lives in a bivalved shell. But this is where the resemblance ends. A simple 'rule of thumb' to distinguish molluscs from brachiopods: in brachiopods the valves differ in shape and size. Posteriorly, the larger valve has a hole through which a pedicle protrudes with which the animal anchors itself to the sea floor. Another typical feature of this group of animals are its ‘lophophores’: often ribbon-like organs serving as gills, but also, with the help of cilia, which channel a stream of water towards the mouth located further away. A brachiopod can thus only live in clear waters: too high a supply of silt or sand leads to 'suffocation'. Nowadays brachiopods are only found in the deeper parts of oceans, for instance in the North Sea at depths of 200 m and below.