Chelicerata is a group of arthropods characterised by a body divided into two parts. The prosoma (upper part) has a tough shell. The opisthosoma (lower part) is very well developed.
This group includes Merostomata (horseshoe crabs) and arachnids (spiders, scorpions, pseudoscorpions and a few other groups). Besides horseshoe crabs (marine animals that dwell on the ocean floor), most chelicerates are land-dwellers.
These animals have chelicerae, a pair of appendages near the mouth, corresponding to the second pair of antenna among mandibulates (crustaceans, insects...). Chelicerae are also found among pycnogonids, small marine animals that look like spiders. Pycnogonids and chelicerates are grouped together in cheliceriforms.