Arachnid a

(a-rak´ni-da; Gr. arachnē , a spider), a cla of Arthropod a or higher Annulose animals including the Spiders, Scorpions, Mites, Ticks, . They have the body divided into a number of segments or somites , some of which have always articulated appendages (limbs, .). There is often a pair of nervous ganglia in each somite, although in some forms (as spiders) the nervous system becomes modified and concentrated. They are oviparous and somewhat resemble insects, but they have a united head and thorax, and do not undergo a metamorphosis similar to insects. They respire by tracheæ, by pulmonary sacs, or by the skin.