Caspian Sea
The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not a freshwater lake. It contains about 3.5 times more water, by volume, than all five of North America's Great Lakes combined. The Caspian was once part of the Tethys Ocean, but became landlocked about 5.5 million years ago due to plate tectonics. The Volga River (about 80% of the inflow) and the Ural River discharge into the Caspian Sea, but it has no natural outflow other than by evaporation. Thus the Caspian ecosystem is a closed basin, with its own sea level history that is independent of the eustatic level of the world's oceans.
Caspian tadpole goby
The Caspian tadpole goby ("Benthophilus macrocephalus") is a species of goby which is widespread in the basin of the Caspian Sea, specifically in the near-estuary zone of the rivers and in small bays. It is a common species in the Volga River delta near Astrakhan, occurred in the deltas of rivers Terek, Ural, Samur. During the warmer months, this species prefers to live at depths of from , moving in the colder months to depths of . It can reach a length of TL.