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Noun A thin organic coating or “skin” which is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among mollusks it is primarily seen in snails and clams, i.e. in gastropods and bivalves, but it is also found in cephalopods such as Allonautilus scrobiculatus. Periostracum is an integral part of the shell, and it forms as the shell forms, along with the other shell layers....

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/ˌpərmēəˈbilitē/ Noun 1. The quality or state of being permeable. ( 2. The property of something that can be pervaded by a liquid (as by osmosis or diffusion). ( (Physics) 1. (Electromagnetism) The property of a magnetizable substance that determines the degree in which it modifies the magnetic flux in the region occupied by it in a magnetic field. ( (Geology) 1. The ability of a rock, soil or sediment to transmit water. ( Word origin: From French...

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/ˈpərmēəbəl/ Adjective 1. Of or relating to substance, substrate, membrane or material that absorbs or allows the passage of fluids. ( 2. (Of a material or membrane) Allowing liquids or gases to pass through it. (Google Dictionary) 3. Capable of being permeated or passed through, used especially of substances where fluids can penetrate or pass through. ( 4. Allowing fluids or gases to pass or diffuse through. ( Word origin: From Late Latin permeabilis “that can be passed through, passable,” from Latin permeare “to pass through, go over,” from per- “through” + meare “to...

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