The Argasidae are the family of soft ticks, one of the two big families of ticks. They lack the hard scutum present in the hard ticks (Ixodidae). The gnathosoma (or capitulum, the mouthparts-bearing structure) is located on the underside of the animal's body and is not readily visible, while in the Ixodidae the gnathosoma projects forward from the body. The family contains 193 species, although the composition of the genera is less certain, and more study is needed before the genera can become stable. The currently accepted genera are Antricola, Argas, Nothoaspis, Ornithodoros, and Otobius.