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The four most universal features defining modern molluscs are a soft body composed almost entirely of muscle, a mantle with a significant cavity used for breathing and excretion, the presence of a radula (except for bivalves), and the structure of the nervous system. Other than these common elements, molluscs express great morphological ...
The tentacle is composed of two distinct structures: the first structure, a fleshy sheath that contains the second structure: an extendable cirrus (plural: cirri). [ 10 ] [ 12 ] The sheaths of the digital tentacles are fused at their base into a single mass referred to as the cephalic sheath.
The taxonomic term Bivalvia was first used by Linnaeus in the 10th edition of his Systema Naturae in 1758 to refer to animals having shells composed of two valves. [3] More recently, the class was known as Pelecypoda, meaning "axe-foot" (based on the shape of the foot of the animal when extended).
This space contains the mollusk's gills, anus, osphradium, nephridiopores, and gonopores. The mantle cavity functions as a respiratory chamber in most mollusks. In bivalves it is usually part of the feeding structure. In some mollusks the mantle cavity is a brood chamber, and in cephalopods and some bivalves such as scallops, it is a locomotory ...
A cross-section of a Nautilus pompilius shell, showing the large body chamber, shrinking camerae, concave septa, and septal necks (partial siphuncle supports) All nautiloids have a large external shell, divided into a narrowing chambered region (the phragmocone) and a broad, open body chamber occupied by the animal in life. The outer wall of ...
The less major anterior and posterior retractor muscles extend from the shell and attach the body to a structure called the foot. [4] This muscular foot is typical of most bivalves, extending anteriorly between the valves (via an anterior protractor muscle) and aiding in locomotion , burrowing and anchorage ( holdfast ).
The lower right portion of this image shows a Venerupis senegalensis with a distinct pallial sinus on the viewer's right side/ animal's right valve which points towards the animal's posterior. The oldest point of a bivalve shell is called the beak, and the raised area around it is known as the umbo (plural umbones). [9]
The name chiton is Neo-Latin derived from the Ancient Greek word khitōn, meaning tunic (which also is the source of the word chitin). The Ancient Greek word khitōn can be traced to the Central Semitic word *kittan , which is from the Akkadian words kitû or kita'um , meaning flax or linen, and originally the Sumerian word gada or gida .