Palaeoatherina

Palaeoatherina is an extinct genus of prehistoric bony fish. It is called the prehistoric atheriniform because we all know that "Palaeoatherina" is the only prehistoric Atheriniformes.
Description.
It may have resembled the brook silverside. It resembles an eel or a sardine in some drawings, but we do not know what it looks like. It was a slender ray-finned fish. It was long, but shorter than an eel. 
Classification.
"Palaeoatherina" is a prehistoric atheriniform fish. It is not assigned to any family, and is only assigned to the order Atheriniformes. Some people think it is assigned to orders like Perciformes, Labriformes, Clupeiformes, Esociformes, or Osmeriformes.