The defining quality of a hermit is that you never see the whole creature. What emerges from the chosen shell may suggest something to you, but inside the shell there is mystery. The hermits do not like to be fully known. They shelter the truth of themselves inside whatever they find that fits. 

They aren’t a species. All kinds of creatures can produce the odd hermit here and there. These are the oceanic introverts, the shy entities that do not want anyone to see their posteriors.

For beach scavengers, a hermit on the shore is always a tempting proposition. The shells can make them easier to catch, and it is sometimes a simple business to cook the entire hermit inside whatever they’ve hidden in. Of course it won’t be until you get the hermit out of the shell that you’ll know if they were worth the effort of baking them.