seashell

seashell
/see"shel'/, n.
the shell of any marine mollusk.
Also, sea shell.
[bef. 900; OE saescill (not recorded in ME) see SEA, SHELL]

* * *

 hard exoskeleton of marine mollusks such as snails, bivalves, and chitons that serves to protect and support their bodies. It is composed largely of calcium carbonate secreted by the mantle, a skinlike tissue in the mollusk's body wall. Seashells are usually made up of several layers of distinct microstructures that have differing mechanical properties. The shell layers are secreted by different parts of the mantle, although incremental growth takes place only at the shell margin. One of the most distinctive microstructures is nacre, or mother-of-pearl, which occurs as an inner layer in the shells of some gastropods and bivalves and in those of the cephalopods Nautilus and Spirula.

      Seashells may be univalved (as in snails) or bivalved (as in clams), or they may be composed of a series of plates (as in chitons). They may also be reduced to small internal plates or granules, as in some slugs. In gastropods, bivalves, and shelled cephalopods, the coiled form of the shell approximates an equiangular spiral or variations of it. In some forms, such as the worm shells (family Vermetidae), however, the coiling of the shell is irregular. Shells are frequently ornamented with complex arrangements of spines, folia, ribs, cords, and grooves, which in some species provide protection against predators, give added strength, or assist in burrowing. The aperture of gastropod shells is particularly vulnerable to predators and may be protected by complex folds and teeth. Many species use a calcareous or horny operculum (trapdoor) on the foot to seal off the aperture when the foot is withdrawn into the shell. In the cephalopods nautilus and Spirula, the planospirally coiled shell consists of multiple chambers connected by a porous tube called the siphuncle. The chambers contain quantities of water and gas that are adjusted by the siphuncle to achieve neutral buoyancy. Many seashells are brightly coloured in complicated designs by a variety of pigments secreted by special cells in the edge of the mantle. In some cases there is an obvious camouflage function, but in most others the significance of the colours is unclear.

      Seashells are collected all over the world because of their endless diversity, elegance of form, and bright colours. (See shell collecting.) They also have been used to make jewelry, buttons, inlays, and other decorative items throughout history. In ancient times certain varieties, such as tooth shells and cowrie shells, were even used as money. See also bivalve; gastropod; nautilus.

* * *


Universalium. 2010.

Нужен реферат?

Look at other dictionaries:

  • Seashell — (Lehigh Acres,США) Категория отеля: Адрес: Lehigh Acres, 33972, США Опис …   Каталог отелей

  • Seashell — Sea shell , n. (Zo[ o]l.) The shell of any marine mollusk. [1913 Webster] …   The Collaborative International Dictionary of English

  • seashell — (n.) also sea shell, O.E. sæscel (see SEA (Cf. sea) and SHELL (Cf. shell) (n.)) …   Etymology dictionary

  • seashell — ► NOUN ▪ the shell of a marine mollusc …   English terms dictionary

  • seashell — [sē′shel΄] n. the shell of any marine mollusk …   English World dictionary

  • Seashell — A seashell, also known as a sea shell, is the common name for a hard, protective outer layer, a shell, or in some cases a test , that was created by a sea creature, a marine organism. The shell is part of the body of a marine animal, in most… …   Wikipedia

  • seashell — 1. noun a) the empty shell of a marine mollusk b) A very light pink colour, like that of some seashell. 2. adjective Of a very light pink colour, like that of some seashell. See Also: scungilli …   Wiktionary

  • seashell — UK [ˈsiːˌʃel] / US [ˈsɪˌʃel] noun [countable] Word forms seashell : singular seashell plural seashells the empty shell of a sea animal …   English dictionary

  • seashell — noun Date: before 12th century the shell of a marine animal and especially a mollusk …   New Collegiate Dictionary

  • seashell — (Roget s IV) n. Common sea shells include: conch, periwinkle, abalone, ammonite, ram s horn, clam, mussel, oyster, starfish, sea urchin, sand dollar, sea snail, nautilus, scallop, cowrie, limpet, cockle, whelk; see also shell 3 …   English dictionary for students

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”