Slugs are gastropods. All slugs are shell-less.
They have internal shells. According to scientists. (more than 3 shells.)
The only extant cephalopod that produces an external shell is the chambered nautilus. The shells produced by squid and cuttlefish are internal.
it's a cuttlefish!
A octopus is a cephalopod that has no shell. Also squid have internal shells that are not used for protection.