Mieridduryn is a genus of extinct dinocarididarthropod that lived during the Middle Ordovician of what is now the United Kingdom. This animal was described in 2022 based on a singular fossil found in Castle Bank, a Burgess shale typelagerstätte located in the country of Wales. This animal's taxonomic affinities are somewhat unclear, but there are some hypotheses. One is that this animal represents a new grade of stem-euarthropods that evolved features similar to the Cambrian aged opabiniids (a family of basal arthropods). Another is that if the features seen in Mieridduryn are convergent, and not homologous, to those seen in radiodonts, then this animal represents a late surviving opabiniid (if the latter option is correct, then this means the opabiniids survived for over 40 million years longer than what was once thought).[1][2][3][4]