Caspian Sea
The wide and endorheic Caspian Sea has a north–south orientation and its main freshwater inflow, the Volga River, enters at the shallow north end. Two deep basins occupy its central and southern areas. These facts lead to horizontal differences in temperature, salinity, and ecology. The Caspian Sea spreads out over nearly 750 miles (1,200 km) from north to south, with an average width of 200 miles (320 km). It covers a region of around 149,200 square miles (386,400 square km)—bigger than the region of Japan—and its surface is about 90 feet (27 meters) below sea level. The sea bed in the southern part reaches as low as 1,023 m (3,356 ft) below sea level, which is the second lowest natural depression on earth after Lake Baikal (−1,180 m, −3,871 ft). The ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its saltiness and large size.
Caspian turtle
"Mauremys caspica" is a tan to blackish, medium-sized, semiaquatic turtle, which may attain a carapace length of . Its low, oval carapace has a slight medial keel (better developed in juveniles) and a smooth, unserrated marginal border, which is slightly upturned and tapered above the tail. A pair of low lateral keels are present on the pleural scutes of hatchlings, but these become lower with age and disappear completely in adults. The carapace is tan to olive or black with yellow to cream-colored reticulations patterning the scutes, and some individuals have yellow vertebral stripes. These light lines fade with age, but the pleural seam borders become darker. The well-developed plastron is notched posteriorly. The plastral formulae are given in the subspecies descriptions under Geographic Variation. The plastron is either yellow with variable reddish to dark-brown blotches, or dark brown or black with a yellow blotch along the lateral scute borders. The bridge is either yellow with dark seam borders and dark spots on the corresponding marginals, or almost totally black with a few small yellow marks. The head is not enlarged, and is olive to dark brown with yellow or pale cream-colored stripes. Some stripes extend anteriorly from the neck onto the head. One of these on each side passes above the eye and onto the snout where it meets the stripe from the other side. Several others extend across the tympanum to contact the posterior rim of the orbit, and two additional stripes continue across the snout and pass ventral to the orbit. The neck, limbs, and tail are tan gray to olive or black with yellow, cream, or gray stripes or reticulations.
"M. caspica" has 52 chromosomes; (Killebrew, 1977a; Bickham and Carr, 1983).
Females are generally larger than males, have flat plastra and shorter tails with the vent under the rim of the carapace. The smaller males have concave plastra and longer, thicker tails with the vent beyond the rim of the carapace.