Editing Arachnid (section)

==Senses==

Arachnids have two kinds of eyes: the lateral and median [[ocelli]]. The lateral ocelli evolved from [[compound eye]]s and may have a [[tapetum lucidum|tapetum]], which enhances the ability to collect light. With the exception of scorpions, which can have up to five pairs of lateral ocelli, there are never more than three pairs present. The median ocelli develop from a transverse fold of the [[ectoderm]]. The ancestors of modern arachnids probably had both types, but modern ones often lack one type or the other.<ref name=pinto2007/> The [[cornea]] of the eye also acts as a lens, and is continuous with the cuticle of the body. Beneath this is a transparent vitreous body, and then the [[retina]] and, if present, the tapetum. In most arachnids, the retina probably does not have enough light sensitive cells to allow the eyes to form a proper image.<ref name=IZ/>

In addition to the eyes, almost all arachnids have two other types of sensory organs. The most important to most arachnids are the fine sensory hairs that cover the body and give the animal its sense of touch. These can be relatively simple, but many arachnids also possess more complex structures, called [[trichobothria]].{{citation needed|date=March 2025}}

Finally, slit sense organs are slit-like pits covered with a thin membrane. Inside the pit, a small hair touches the underside of the membrane, and detects its motion. Slit sense organs are believed to be involved in [[proprioception]], and possibly also hearing.<ref name=IZ/>