Webster’s Revised Unabridged Dictionary · 1913
Leptocardia
Lep′to·car′di·a (lĕp′tō·kär′dĭ·ȧ), n. pl. [NL., fr. Gr. λεπτός small + καρδία the heart.] (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. [Written also Leptocardii.]