Genus: Archaeonectrus NOVOZHILOV, 1964
Etymology: Greek, arkhaios, “ancient” and Greek, nektris, “swimmer”: Ancient swimmer.

Species: rostratus (OWEN, 1865) NOVOZHILOV, 1964
Etymology: Latin, rostris, rostralis, rostrum, "beak, snout."
= Plesiosaurus rostratus OWEN, 1865

Holotype: BMNH 38525

Locality: Lyme Regis coast, Pinhay Bay- Charmouth, (SY 3291-SY 3794), Dorset County, England, Southern United Kingdom.

Horizon: Lower Lias.

Biostratigraphy: Arietites bucklandii zone.

Age: Lower Sinemurian Stage, Lower Lias Epoch, Early Early Jurassic.

Material: Skull and skeleton.

Referred material:

BROWNE, 1894

Locality: Aust Cliff, Avon (ST 565895-ST 572901, Bristol, Gloucestershire County, England, Southern United Kingdom.

Horizon: Westbury Formation, ‘Rhaetic bone bed’.

Biostratigraphy:

Age: Rhaetian Stage, Uppermost Late Triassic Epoch, Late Triassic.

Material:

Number: Not given: Teeth.