Assertion: gastropod's shell | /r/MadeOf | protein
Facets:
Source sentences:
text: Sea slugs, like nudibranchs and sea hares, do not have a shell, although they may have an internal shell made of protein.
text: No external shell; soft internal shell made of protein
text: This has a single, "limpet-like" shell on top, which is made of proteins and chitin reinforced with calcium carbonate.
text: This has a single, "limpet-like" shell on top, which is made of proteins and chitin reinforced with calcium carbonate, and is secreted by a mantle covering the whole upper surface.