Petromyzontiformes

noun

No bone; seven pairs of external lateral gill openings; eyes lateral (except in Mordacia; tail isocercal in adults, hypocercal in ammocoete larvae; body naked, eel-like; no paired fins.

The Order Petromyzontiformes belongs to the Class Cephalaspidomorphi (lampreys). It contains 1 Family. The Order is most closely related to the Order Chimaeriformes; these Orders shared a common ancestor 455 million years ago. Members of this Order have been dated back to the Ordovician period. Etymology of this Order name: Latin, petra = stone + Greek, myzo = to suckle + Latin, forma = shape.