||Lep`to*car"di*a (l&ebreve;p`t&osl;*kär"d&ibreve;*&adot;), n. pl. [NL., fr. Gr. lepto`s small + kardi`a the heart.] (Zoöl.) The lowest class of Vertebrata, including only the Amphioxus. The heart is represented only by a simple pulsating vessel. The blood is colorless; the brain, renal organs, and limbs are wanting, and the backbone is represented only by a simple, unsegmented notochord. See Amphioxus. [Written also Leptocardii.]