This series of four shakers depict what are called "Kappas". They are Japanese folklore - it is an amphibious imp that are typically depicted as green, human-like beings with webbed hands and feet and a turtle-like carapace on their backs. These have to be some of the cuter examples of Kappas I could find.
They were first described by Irene Thornburg in her The Big Book of Salt & Pepper Shakers Series on page 132. They stand 3.75 inches tall, have 3 and 2 pour holes, and often have a "Quality Product of Japan" foil label.