\Lep`to*car"di*a\ (l[e^]p`t[-o]*k[aum]r"d[i^]*[.a]),
n. pl. [NL., fr. Gr. lepto`s small + kardi`a the heart.]
(Zo["o]l.)
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}.]