Covered by chitinous exoskeleton. Food tube simple. Mouth at anterioventral end. Haemocoel of blood sinuses with a dorsal heart. Usually the circumesophagial ring and ventral cords united into brain from which nerves issue directly.
Eggs are centrolecithal.
Development does not include larval form that is markedly different from adult. B Taxonomy of the Phylum. Limulus, Carcinoscorpius, Tachypleus. Centuroides, Acanthophrynus, Charinus, Mastigoproctus, Thelyphonus, Prokoenenia, Koenenia, Miranda, Latrodectus, Lycosa, Argiope, Eremobates, Galeodes, Chelifer, Cryptocellus, Ricinoides, Phalangium, Leioburnum, Dermacentor, Trombicula.