How do shells get their shape?

Shells come in so many amazing shapes and sizes -  spirals, sand dollars, sundials, ones that whirl around, ones that twirl around, ones that twist to the side and some that even look like cookies! Our listener Lily had a great question about these shapes, and Mike Sanchez, a Naturalist at the New Mexico Museum of Natural History and Science, helps us get to the bottom of this twisted subject!

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