Leptocardia
Leptocardia (lep`to*kar"di*ȧ) , noun, plural
[New Latin, from Greek lepto`s small + kardi`a the heart.]
(Zoology) 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.