The embryonic shell, or first chamber, of ammonites and other cephalopods.

See "nuclear whorls."

Literally the 'first shell'. This is the initial chamber of the phragmocone and in living cephalopods is produced before the animal hatches from the shell. The shape and size of the protoconch is important in classifying ammonites.

the apical whorls of a shell usually characterised by sculptural differences from the rest of the shell or teleoconch; the protoconch is formed while the individual is in the egg

A protoconch is an embryonic or larval shell of a mollusc, e.g., the initial chamber of an ammonite. It may consist of several whorls.