Shell is internal inA. LoligoB. ChitonC. DentaliumD. Unio

Shell, in the context of mollusks, refers to the hard outer protective covering that many mollusks possess. Among the options you've provided, the mollusks that typically have a shell are:

A. Loligo - Loligo is a genus of squid, and squids do not have an external shell. They have an internal structure known as a pen, which is a vestige of a shell.

B. Chiton - Chitons are mollusks that indeed have a shell. Their shell is composed of multiple overlapping plates or valves that provide protection to their soft body.

C. Dentalium - Dentalium is a genus of tusk shells, which are also mollusks with a slender, tubular shell. The shell is often open at both ends.

D. Unio - Unio is a genus of freshwater mussels, and mussels are mollusks that possess a shell made up of two hinged halves.

So, the correct answer is:

B. Chiton