||Gna*thos"to*ma (?), n. pl. [NL., from Gr. gna`qos the jaw + &?;, &?;, the mouth.] (Zoöl.) A comprehensive division of vertebrates, including all that have distinct jaws, in contrast with the leptocardians and marsipobranchs (Cyclostoma), which lack them. [Written also Gnathostomata.]