Gynodiastylidae is one of the eight most commonly recognised families of crustaceans of the order Cumacea.

They are especially prevalent in the southern hemisphere, with some types described from Japan, Thailand and the Persian Gulf.

[3] Gynodiastylidae have a small free telson, usually lacking terminal setae, though in some cases there may be two.

The first pereopods have a group of long rigid fibres (setae) on the propodus.

Because they lack exceptions to the two most important diagnostic characteristics (the lack of pleopods in males and of exopods on maxilliped 3 in females), Gynodiastylidae have a pre-eminent place among monographic descriptions.