Assertion: cephalopod's shell | /r/MadeOf | chitin
Facets:
Source sentences:
text: Although the squids lack exterior shells they have a vestigial shell inside, made of chitin.
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.