Are hermit crabs arthropods or mollusks?

Hermit crabs are arthropods.

Here's why:

* Arthropods have a hard exoskeleton made of chitin, jointed legs, and a segmented body.

* Mollusks have a soft body, often with a shell, and a muscular foot.

Hermit crabs clearly fit the description of arthropods:

* They have a hard exoskeleton.

* They have jointed legs (ten in total).

* They have a segmented body.

While hermit crabs do use empty mollusk shells for protection, this doesn't make them mollusks. They are arthropods that have adapted to use a unique form of shelter.