Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun The tough horny or fibrous outer covering of the shell of many mollusks and brachiopods.

from The Century Dictionary.

  • noun The horny epidermal investment of the shells of most mollusks.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Zoöl.) A chitinous membrane covering the exterior of many shells; -- called also epidermis.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun malacology The proteinaceous outer sheath of many molluscan shells.

Etymologies

from The American Heritage® Dictionary of the English Language, 4th Edition

[New Latin : peri– + Greek ostrakon, shell; see ost- in Indo-European roots.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

Literally "surrounding shell," from peri- +‎ ostracum.

Examples

  • The researchers compare it to the thin protein coating, called the periostracum, seen on the shells of other snail species.

    Breaking News: CBS News

  • The researchers compare it to the thin protein coating, called the periostracum, seen on the shells of other snail species.

    Blah, Blah! Technology

  • The researchers compare it to the thin protein coating, called the periostracum, seen on the shells of other snail species.

    British Blogs

  • The researchers compare it to the thin protein coating, called the periostracum, seen on the shells of other snail species.

    Discover Blogs

  • [2] This shell has an outer tissue-like layer called the periostracum that changes color as the bicuspid grows.

    CreationWiki - Recent changes [en]

  • [2] This shell has an outer tissue-like layer called the periostracum that changes color as the bicuspid grows.

    CreationWiki - Recent changes [en]

  • Is their periostracum sticky or is the snails' mucus somehow involved in the process?

    Gastrocopta contracta

  • However, one problem with ink is that it isn't absorbed into the periostracum but stays on it and, sooner or later, even the most "permanent" ink flakes off.

    Archive 2008-08-01

  • However, one problem with ink is that it isn't absorbed into the periostracum but stays on it and, sooner or later, even the most "permanent" ink flakes off.

    How to mark a snail shell

  • Gastrocopta that I've run across are often in more xeric habitats - perhaps there's a combination of fluctuating moisture in the soil and the snail's ecology some are burrowers that tends to get soil stuck to the periostracum.

    Gastrocopta contracta

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