Lungs are present but greatly reduced in some species. An ypsiloid cartilage is present. Larvae have four pairs of gill slits and large external gills. The scapula and coracoid bones of the pectoral girdle are fused to form the scapulocoracoid. Vertebral centra are opisthocoelous.
Ribs are bicapitate.
Spinal-nerve foramina are present in neural arches of all vertebrae except for spinal nerves exiting between the atlas and first trunk vertebra. The pubotibialis and puboischiotibialis exist as separate muscles. Anterior glomeruli of the kidney are reduced or absent. Reproductive characters Fertilization is internal. Ciliated epithelium may be present or absent in the cloacal tube and anterior cloacal chamber of females.