Composed of the spiders, scorpions, ticks, mites and allies; Largest and most important chelicerates
Nervous organs
sensory hairs (trichobothria), eyes, and slit senses
Body segments
cephalothorax and abdomen
○ "Head” portion has sensory hairs and eyes (compound and simple)
○ 4 appendages attached to cephalothorax; the two anterior pairs for feeding and the rest for movement.
○ Abdomenhas minute pore openings (spiracles), leads to internal lamellae called book lungs
Circulation
heart → dorsal anterior & posterior aorta → small arteries → tissue spaces/sinuses → large ventral sinus → book lungs → venous channels → pericardium → ostia → heart
Excretion
coxal glands-thin-walled spherical sacs along the sides of the prosoma that collect wastes from the surrounding blood
Reproductive
Dioecious, has single or paired gonads in the abdomen, sperm transfer is indirect and through spermatophores, and ducts exit through the genital orifice.
Nervous System
Protocerebrum- contains the optic centers and optic nerves
Tritocerebrum- contains the nerves supplying the chelicerae