Assertion: coral's skeleton | /r/HasProperty | hard
Facets:
Source sentences:
text: Corals secrete a hard skeleton, called a corallite, under their skin.
text: The skeleton of a black coral is hard and inert, due to its composition of protein and chitin, making it nearly inedible.
text: In both stony and soft corals, the polyps can be retracted by contracting muscle fibres, with stony corals relying on their hard skeleton and cnidocytes for defence.