Actin in Miliammina fusca (Brady) was identified by immunoblotting with a monoclonal antibody and compared to the actin of other foraminifera, including porcellaneous-walled Miliolina and agglutinated-walled Textulariina. M. fusca possesses one actin band (which molecular weight averages 46 kD), that is similar to the other Miliolina, but clearly differs from the two actin bands (at about 43 and 45 kD) observed in the other foraminifera. This result suggests a close relationship of M. fusca with porcellaneous foraminifera in contrast to modern taxonomy which places this species within the agglutinated foraminifera.