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

[2] Diastylidae have a medium to large, free telson, that has not fused with the last pleon segment.

[3] Males have generally two pairs of pleopods, though in rare cases they may be rather small or even entirely absent.

[3] The interior branch of the uropods are generally made up of two or three segments, but in some rare case may have just one.

Members of this family frequently show clear sexual dimorphism.