Order Synhymeniida de Puytorac et al., 1974

Fam. Orthodonellidae Jankowski, 1968

Fam. Nassulopsidae Deroux in Corliss, 1979

Fam. Scaphidiodontidae Deroux, 1978

Fam. Synhymeniidae Jankowski in Small & Lynn, 1985