Spiroplasmas is an evolutionarily interesting group of bacteria belonging to the class Mollicutes.They have small size and helical structure, lack of a cell wall, and have special motility.Spiroplasma eriocheiris is a novel pathogen of aquatic crustaceans and it was first found in Chinese mitten crab Eriocheir sinensis associated with tremor disease and then found in almost all economically crustaceans, which brought serious damage to aquaculture worldwide.