arachnida(n = noun.animal) class arachnida - a large class of arthropods including spiders and ticks and scorpions and daddy longlegs; have four pairs of walking legs and no wings;
is a kind of class
is a member of chelicerata, superclass chelicerata
Derived form adjective arachnidian₁

   One of the classes of Arthropoda. See Illustration in Appendix. [1913 Webster]
" They have four pairs of legs, no antennæ nor wings, a pair of mandibles, and one pair of maxillæ or palpi. The head is usually consolidated with the thorax. The respiration is either by trancheæ or by pulmonary sacs, or by both. The class includes three principal orders: Araneina, or spiders; Arthrogastra, including scorpions, etc.; and Acarina, or mites and ticks." [1913 Webster]

class arachnida