Protoconch

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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.

The teleoconch (the whorls of an adult shell after the protoconch whorls) may be visibly separated from the protoconch and even spiral in the opposite direction. In the latter case the protoconch is called heterostrophic.

The first part of the protoconch that is formed within the embryonic egg capsule is called protoconch 1 while the part that is formed after the larva has hatched is called protoconch 2. Protoconch 1 and 2 often have different ornamentation and can be distinguished by microscopy. The teleoconch is formed after the larva has settled and become a juvenile. The structure of the protochonchs are widely used in gastropod systematics. The homologous structure in bivalves is called prodissoconch.