Petromyzontiformes
General description:
The order Petromyzontiformes comprises a single family, Petromyzontidae, which contains 40 extant species of lamprey divided into 10 genera.
Diagnostic description:
Lack a bony skeleton and jaws (bones may have been secondarily lost, as there is evidence to suggest that their ancestors possessed a bony skeleton).
No paired fins (pectoral, pelvic), but dorsal and caudal (tail) fins present.
Horny teeth are used as a "rasping tongue" to suck on to prey, and pierce the flesh to draw blood.
Water flows in and out of the paired gill openings in a tidal flow - most fish draw water into the mouth,over the gills, and out through the gill slits.