Leptocardia /(lĕp`tō̇*kär"dĭ*ȧ)/

Lep·to·car·di·a

Leptocardia

n. pl.
  1. 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. (Zool.)