Medical Dictionary
Arachnida
noun pl Arach·ni·da \ə-ˈrak-nəd-ə\
Medical Definition of ARACHNIDA
: 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
—arach·nid \-nəd\ adjective or noun
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