Promissum

Promissum is an extinct genus of conodonts, primitive chordates, that lived during the Upper Ordovician period.
A conodont, "Promissum" had a primitive mouth under its eyes with mineralized teeth, which are both typical for conodonts. It had a primitive backbone and probably looked like a small eel or large worm, lacking any kind of fins except for perhaps a small one on the tail. It was relatively large for a conodont, reaching about 40 cm (16 inch) in length.
Well-preserved specimens were discovered in the Soom shale of South Africa in 1994.
"Promissum" was probably capable of maintaining a cruising speed, but not of bursts of speed.