Crymostygius thingvallensis

This small amphipod is unique to the area around Lake Thingvallavatn in southwestern Iceland. Found in spring inlets, it is the only place in the world where this species lives. It is a stygobiont, meaning that it lives in the groundwater system.
The species apparently survived Pliocene and Pleistocene glaciations in the groundwater of a porous lava and may have persisted in Iceland for several million years. The name is drawn from the Greek word crymos meaning ice or frost and the name of the river Styx, referring to subterranean waters, indicating that the family encompasses species that have survived glaciations in subterranean waters.
Amphipods are among the most species-rich peracarid groups with over 7000 known species. This species can reach a length of 22 mm, with a long and slender unpigmented body.