leptocardii

Century Dictionary and Cyclopedia

1. The lowest group of true vertebrates; a class or other high division of Vertebrata, to which different values have been assigned by naturalists; the lancelets. In the leptocardians the skeleton is notochordal, acranial, and membranocartilaginous; they have no brain, no jaws, contractile pulsating sinuses instead of a heart, colorless blood, confluent respiratory and abdominal cavities, and many branchial clefts through which water enters to be expelled by an opening in front of the vent. In the older systems the group was considered an order of fishes; by Johannes Muller and others, a subclass of fishes; now, it is generally rated as a separate class of Vertebrata. Other names of the same group, in some of its acceptations, are Cirrostomi, Pharyngobranehii, Acrania, Entomocrania, Cephalochorda, and family Branchiostomidæ or Amphioxidæ. Only about six species are known. Also Leptocardia. See cuts under Branchiostoma and lancelet.