I am not sure of the definition of a living fossil, but maybe Analetris eximia, found in the Saskatcherwan River and described as a new genus and species by Edmunds and Koss, qualifies as a living fossil. See details on the species as I know it here 1/5 down from top of page.
Important points, comparing the existing and fossil species, from above:
1. The fossil is in Eocene Baltic Amber, and thus probably considered to be 45-50 million years old.
2. The fossil is so close to the existing species found in the river that the authors use rather minute technical morphological details to show that the fossil is a new species, and not the same as the existing species. Thus, the fossil species and living species are almost identical except for small details (see pdfs, above).
3. The genus Analetris is now considered to be North American. The fossil is from the Old World, where it is not now found.