Chitin is present in all arthropods (A-19 through A-21),
as well as in pogonophoran (A-25), annelid (A-22), brachiopod
(A-30), and some echiuran (A-24) setae (bristles); in onychophoran
cuticle (A-28), the radula (rasping organs) of molluscs
(A-26), and cell walls of fungi and red algae (Pr-33); and in
chytrid cell walls (Pr-35). Thus, chitin by itself is not a reliable
indicator of evolutionary relationships.