Gnathostoma \Gna*thos"to*ma\, n. pl. [NL., from Gr. gna`qos the
jaw + ?, ?, the mouth.] (Zool.)
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}.]