Assertion: giant clam's number | /r/MadeOf | chitin
Facets:
value: mainly
type: DEGREE
Source sentences:
text: The mantle edge secretes a shell (secondarily absent in a number of taxonomic groups, such as the nudibranchs) that consists of mainly chitin and conchiolin (a protein hardened with calcium carbonate), except the outermost layer, which in almost all cases is all conchiolin (see periostracum).