Arachnida

noun plural

Arach·​ni·​da ə-ˈrak-nəd-ə 

: a large class of arthropods that are mostly air-breathing by means of trachea or book lungs, that include the spiders and scorpions, mites, and ticks, and that have a segmented body divided into two regions of which the anterior bears four pairs of legs but no antennae

arachnid

-nəd 

adjective or noun