No antennae . The first pair of appendages are the chelicerae , which they use to catch and pierce their prey. The second pair of appendages are the pedipalps , which vary greatly among groups and which can be used in prey capture. Some are marine and some are terrestrial. Compound eyes present.
Book gills for respiration.
Dorsal side covered with a carapace . Simple eyes present. Only a vestigial abdomen present. No respiratory or excretory system. Spiders, scorpions, pseudoscorpions, ticks, mites.