How many letters does the top answer for “one of the coiled chambered fossil shells of extinct mollusks” have?

The most common answer is ammonite (8 letters).

Crossword clue: one of the coiled chambered fossil shells of extinct mollusks

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

ammonite 8 letters wn-def

one of the coiled chambered fossil shells of extinct mollusks

ammonoid 8 letters wn-def

one of the coiled chambered fossil shells of extinct mollusks