1. None
2. None
3. Chelicerae (pinchers)
4. Legs or pedipalps
5. Legs
6. Legs
7. Legs
8. Legs
The legs on the prosoma are either uniramous or have a very reduced gill branch, and are adapted for walking or swimming. The appendages on the opisthoma, in contrast, are either absent or are reduced to their gill branch.
The Cheliceriformes are divided into three classes:
The last of these actually have very strong differences from the body plan described above, but are placed here because they have chelicerae and do not show any clear relationship to any other arthropods. The Merostomata are found in the fossil record from the Ordovician onwards, and when young show some resemblance to the Trilobita, suggesting a possible relationship between these and the Cheliceriformes.