leptocardia

from The Century Dictionary.

• Same as Leptocardii.

from the GNU version of the Collaborative International Dictionary of English.

• noun plural (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.