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When the word "seashells" refers only to the shells of marine mollusks, then studying seashells is part of conchology.Conchologists or serious collectors who have a scientific bias are in general careful not to disturb living populations and habitats: even though they may collect a few live animals, most responsible collectors do not often over-collect or otherwise disturb ecosystems.
The larval shell may have a completely different mineralogy to the adult conch, perhaps formed from amorphous calcite as opposed to an aragonite adult conch. [ 2 ] In those shelled molluscs that have indeterminate growth , the shell grows steadily over the lifetime of the mollusc by the addition of calcium carbonate to the leading edge or opening.
The bodies of adult sand dollars, like those of other echinoids, display radial symmetry. The petal-like pattern in sand dollars consists of five paired rows of pores. The pores are perforations in the endoskeleton through which podia for gas exchange project from the body. The mouth of the sand dollar is located on the bottom of its body at ...
Instead, a segmented shell gland forms on one side of the larva, and a foot forms on the opposite side. When the larva is ready to become an adult, the body elongates, and the shell gland secretes the plates of the shell. Unlike the fully grown adult, the larva has a pair of simple eyes, although these may remain for some time in the immature ...
Body whorl—The most recently formed whorl of a spiral shell, in which most of the body of the animal is found; Nuclear whorl(s)—small, generally smooth whorls formed within the egg, and constituting the apex of the shell; Protoconch—a larval shell of a mollusc; also refers to protoconch whorls of an adult shell
The shells of surf clams show growth rings and can demonstrate changes in the environment of the individual. The shells are formed by calcification, as the clam deposits calcium carbonate into the shell via either diet or metabolism. Pausing of growth due to internal or external factors appear marked by dark lines of growth on the shell.
Depending on species, adult shell diameter is between 10 and 25 cm (4 and 10 inches). Nautilidae, both extant and extinct, are characterized by involute or more or less convolute shells that are generally smooth, with compressed or depressed whorl sections, straight to sinuous sutures, and a tubular, generally central siphuncle . [ 5 ]
While metamorphosis is the usual state in molluscs, the cephalopods differ in exhibiting direct development: the hatchling is a 'miniaturized' form of the adult. [42] The development of molluscs is of particular interest in the field of ocean acidification as environmental stress is recognized to affect the settlement, metamorphosis, and ...