Why are mites and ticks the closest relatives of the spider?

Mites and ticks are the closest relatives of the spider because they all belong to the family of Arachnids or joint-legged animals (eight legs), spiders being the largest order in the class. Mites and ticks also belong to this class. The three are closest relatives since, unlike other insects which belong to the same class,  they all breathe using spiracles. 

loss of sensation to pressure and touch

the dorsal column–medial lemniscus pathway (dcml) (also known as the posterior column-medial lemniscus pathway (pcml)) is a sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints.