The accumulation of ions is driven by ion pumps packed within the calcifying epithelium. :РІР‚Р‰475 The periostracum acts as a framework from which the outer layer of carbonate can be suspended, but also, in sealing the compartment, allows the accumulation of ions in concentrations sufficient for crystallization to occur. This caps off the extrapallial space, which is bounded on its other surfaces by the existing shell and the mantle. The shell is deposited within a small compartment, the extrapallial space, which is sealed from the environment by the periostracum, a leathery outer layer around the rim of the shell, where growth occurs. The shell formation requires certain biological machinery. This organic framework controls the formation of calcium carbonate crystals (never phosphate, with the questionable exception of Cobcrephora ), and dictates when and where crystals start and stop growing, and how fast they expand it even controls the polymorph of the crystal deposited, controlling positioning and elongation of crystals and preventing their growth where appropriate. The organic constituent is mainly made up of polysaccharides and glycoproteins its composition may vary widely: some molluscs employ a wide range of chitin-control genes to create their matrix, whereas others express just one, suggesting that the role of chitin in the shell framework is highly variable it may even be absent in monoplacophora. The mantle edge secretes a shell which has two components. When conditions improve again and the mantle resumes its task, a 'growth line' is produced.

When the animal encounters harsh conditions that limit its food supply, or otherwise cause it to become dormant for a while, the mantle often ceases to produce the shell substance. Any injuries to or abnormal conditions of the mantle are usually reflected in the shape and form and even color of the shell. The mantle is visible between the open valvesР”Р„ mollusc shell is formed, repaired and maintained by a part of the anatomy called the mantle.

The giant clam ( Tridacna gigas) is the largest extant species of bivalve. Within some species of molluscs, there is often a wide degree of variation in the exact shape, pattern, ornamentation, and color of the shell. Malacology, the scientific study of molluscs as living organisms, has a branch devoted to the study of shells, and this is called conchology-although these terms used to be, and to a minor extent still are, used interchangeably, even by scientists (this is more common in Europe). Today, over 100,000 living species bear a shell there is some dispute as to whether these shell-bearing molluscs form a monophyletic group (conchifera) or whether shell-less molluscs are interleaved into their family tree.

The ancestral mollusc is thought to have had a shell, but this has subsequently been lost or reduced on some families, such as the squid, octopus, and some smaller groups such as the caudofoveata and solenogastres. Not all shelled molluscs live in the sea many live on the land and in freshwater. We've arranged the synonyms in length order so that they are easier to find.The mollusc (or mollusk ) shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. Synonyms, crossword answers and other related words for CRACKWe hope that the following list of synonyms for the word crack will help you to finish your crossword today. CRACK 'CRACK' is a 5 letter word starting with C and ending with K Crossword clues for 'CRACK' Clue

Its shell does not crack crossword