Family of ticks (superfamily Ixodoidea, order Acarina), the soft ticks, so called because of their wrinkled, leathery, tuberculated appearance that fills out when the tick is engorged with blood. A dorsal shield (scutum) is not present; the mouthparts (capitulum) are subterminal or ventral in a depression (camerostome) that extends above the capitulum to form the anterior margin of the cephalothorax (hood). Argasidae contains 4 genera: Argas, Ornithodoros, Otobius, and Antricola; argasid ticks, chiefly species of Ornithodoros, harbor and transmit spirochetes of the genus Borrelia that cause relapsing fever in birds and mammals.