Tricleidus seeleyi was named by Andrews (1909). Its type specimen is BMNH R3539, a set of limb elements (Shoulder girdle), and it is a 3D body fossil. Its type locality is Hicks and Gardner No. 2 brick pit, Fletton, which is in a Callovian marine horizon in the Oxford Clay Formation of the United Kingdom. It is the type species of Tricleidus.