Even older than dinosaurs, horseshoe crabs evolved more than 400 million years ago at the same time as arthropods like the trilobite. Although their common name indicates that they are a form of crab, this is only due to their external appearance, which has changed little since their ...
Hermit crab, any crab of the families Paguridae and Coenobitidae (order Decapoda of the class Crustacea). These crabs use empty snail shells (e.g., whelk or periwinkle) or other hollow objects as a shelter for partial containment and protection of the bo