Lyrarapax
Lyrarapax is a radiodont genus of the family Amplectobeluidae that lived in the early Cambrian period 518 million years ago. Its fossils were found in the Maotianshan Shales of China. The first species, Lyrarapax unguispinus was described in 2014, with a second species, Lyrarapax trilobus being described in 2016, differing principally in the morphology of its frontal appendages.
Description
L. unguispinus is roughly long. Its frontal appendages are short with a large first endite bearing several spines and alternating endites thereafter. The neck is prominent with four segments. The first flap pair is hypertrophied and paddle-shaped, with the following pairs decreasing sharply in size and a tail fan composed of three blade-like flap pairs. Remarkably, the nervous system of L. unguispinus is preserved in detail, showing that radiodont frontal appendages are protocerebral like the antennae of velvet worms, showing the two structures derive from the same source. In addition, as the labrum also seems to be protocerebral, it also likely derives from the same structures, providing a possible answer to the arthropod head problem.L. trilobus is quite similar, although somewhat smaller, with its H-element having a rimmed margin. The frontal appendages are quite different, with the very presence of endites being alternating and the second endite being especially large. Contrary to its initial description reporting an unusual wrinkled structure around the mouth, Lyrarapax possessed a typical radiodontan oral cone, a radial mouth with four large plates and smaller, thinner plates between them. The first flap in this species is not much wider than the rest, unlike in L. unguispinus, alongside the flaps having transverse lines interpreted as strengthening rays, another trait unique to this species. The trunk is divided into three lobes by prominent furrows, with the central region being more raised than the lateral ones.