Unionopterus

Unionopterus is a genus of eurypterid, an extinct group of aquatic arthropods known as sea scorpions, described in 1948 by the Ukrainian paleontologist Boris Chernyshev from a single fossil found in the Karaganda Formation of Kazakhstan. Its one species, Unionopterus anastasiae, dates to the Early Carboniferous period and was a very small eurypterid, with an estimated body length of only about 2.38 centimeters excluding missing parts. The genus is currently placed in the family Adelophthalmidae, though its classification has been debated because the original description relied on poor illustrations and the only known specimen is presumed lost.