13. The gastropod that lacks a shell is the

a. Cuttlefish

b. Nudibranch

c. Nautilus

d. Squid

Best Option: (D) Squid

Explanation:

Each of these animals has a shell. The cuttlefish, Nudibranch and Nautilus all have shells on the outside of their bodies. The squid does not have a shell on the outside of their body, but it has an internal shell. This is called a pen.

Each of these animals has a shell, but the only one that has an internal shell is the squid.