Source : Webster's Revised Unabridged Dictionary (1913)

Leptocardia \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}.]