There are over 800 species of hermit crabs worldwide, and almost all are ocean dwellers—though people are likely most familiar with the dozen semi-terrestrial species, called land hermit crabs ...

3. Freshwater Crabs Thrive on Land and Water There are many varieties of freshwater crabs that do well in aquariums. Keep in mind, however, that many species need a means of reaching the surface ...

and horseshoe crabs. Traditionally, arachnids were considered a terrestrial monophyletic group—meaning they descended from a single colonization event of land by a terrestrial ancestor.