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Nelson, J.S., 1994

Petromyzontiformes lampreys

Cephalaspidomorphi

Chimaeriformes 455 M years

Forey, P. and P. Janvier, 1993  |  Helfman, G., B. Collette and D. Facey, 1997

late Ordovician

Seewasser

Süsswasser

Brackwasser

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.

Greek, Kephale = head + Greek, aspidos = shield + Greek morphe= shape. Ref. 45335.

Latin, petra = stone + Greek, myzo = to suckle + Latin, forma = shape (Ref. 45335).

( n = 1 ) -
Geotriidae Mordaciidae Petromyzontidae

Ref.
[ e.g. 9948]                       

Glossary
                    [ e.g. cephalopods]