Claim: The family is characterised by several traits, most species possess a groove or furrow ("sulcus") on the dorsal surface between the keels (paranota) on each segment, while in females, the opening on the underside of the body where the gonopods (male reproductive appendages) attach has a central constriction, forming the shape of an hourglass or dumb-bell.
Evidence: In males, the opening on the underside of the body where the gonopods (male reproductive appendages) attach has a central constriction, forming the shape of an hourglass or dumb-bell.