You would need to be a little more specific since there are numerous animals that have shells, particularly sea creatures. While it may be noted that a number of sea animals produce exoskeletons, in general only those of molluscs (which is also spelled as "mollusk") would be typically deemed "sea shells". The phylum Mollusca includes a range of sea animals such as from tiny snails, squid, typical clams and the octopus.
While they are not "shells" when considering the proper sense of the term, you will find that various other animal taxa have exoskeletons.
For instance many anthropods would be thought of as having shells including insects and arachnids. Of course you know that turtles, tortoises as well as terrapins are thought to have 'shells'.
While they are not "shells" when considering the proper sense of the term, you will find that various other animal taxa have exoskeletons.
For instance many anthropods would be thought of as having shells including insects and arachnids. Of course you know that turtles, tortoises as well as terrapins are thought to have 'shells'.