The space between external and internal shells of the main dome was filled with hollow clay resonators.

Nautiluses are the only extant cephalopods which have an external shell.

The external shell is the only significant distinction of material these domes possess.

"You have a strong external shell, but the inside is software and completely vulnerable."

Internal chambers meet the external shell at a boundary known as a "suture line."

Nautiluses are the only cephalopods who have an external shell.

Nautiluses are the only extant cephalopods with an external shell.

Perhaps a human being within an external shell, the upper arms controlled by waldos?

The external shell gives the crustaceans the problem it gave the trilobites.

It has a small ear-shaped, external shell, less than 1 cm long, at the tail end of the mantle.