They differ from suborder Cryptobranchoidea as the angular and prearticular bones in their lower jaws are fused, their trunk ribs are bicapitate, and all members use internal fertilization. The female is fertilized by means of a spermatophore, a sperm-containing cap  placed by the male in her cloaca.
They differ from suborder Cryptobranchoidea as their lower jaw bones are fused, their trunk ribs have two heads, and all members reproduce internally. The female is fertilized by a spermatophore, a sperm-containing cap deposited by the male in her cloaca.