A large animal, the Hydraptor is up to 1.5m long. Its finspan can be 70cm.
It has a large, toothed maxilliped either side of its wide mouth, and two well developed eyes above that. The chemoreceptors on its neck are modified, so they can detect pressure differences around them as well as chemicals.
The Hydraptor has a sophisticated gill around its neck, which uses a counter-current system to supply the animal with oxygen.
It has six well-muscled flippers, which enable it to reach speeds up to 30km/h in the water.
The tail is long, and the anus ejects a compacted mixture of uric acid and faeces.
Hydraptors hunt singly, but in the mating season many hundreds gather near coasts. The largest and strongest, as determined by ritual sizing up of males, get the most females to impregnate.
Gestation takes three months. Hydraptors are ovoviviparous.