Theora mesopotamica

The shell is small and thin, with unequally sized and asymmetric valves. It is about 1.5 times as long as high, rounded in the front, subtruncate behind and moderately swollen in the central region. The umbos are small and point out slightly; they are situated nearer to the anterior than the posterior end. The dorsal margin from the umbo to the upper end of the anterior margin is slightly convex, and from the umbo to the posterior region is straight and sloping. The lower margin is convex and evenly curved, and the surface of the upper part of the shell is striated with fine, irregular, transverse concentric markings. The right valve measures 8.5 mm (0.33 in) in breadth and 5.5 mm (0.22 in) in height, and the right valve 8.0 mm (0.31 in) and 5.4 mm (0.21 in).

Although the species was first found only as subfossil remains by Annandale, he believed it was probably not extinct, and that some of the deposits he saw were likely recent in age. Living specimens of the species have since been obtained from the northwestern part of the Persian Gulf, including in "muddy and silty substrates" around Failaka Island of Kuwait. Within Iraq, Annandale collected his specimens from a sandy lake-bed deposit, in the vicinity of Nasiriyah on the Euphrates. Eames and Wilkins found the species in borings made in the Hammar Marshes, and Plaziat and Younis found it in other localities of the Hammar Formation; they described it as a typical species of this formation. The deposits in Iraq where the species has been found are in brackish habitat (although Annandale believed the deposits to be freshwater, this was due to reworking), toward the outer edge of tidal influence in the Euphrates and Tigris. Much of the species' former habitat, as evidenced by subfossil remains, is now less brackish than it was when the fossils were deposited, meaning it is less likely to be extant in such places.

In a study of fish diets in the Khor Al Zubair, this species was one of the two principal species of bivalve found in the stomach contents of common fish such as soles and croakers.