ACVR1B also transduces signals of nodal, GDF-1, and Vg1; however, unlike activin, they require other coreceptor molecules such as the protein Cripto.
The passage describes ACVR1B as a receptor that receives signals from various molecules (nodal, GDF-1, and Vg1).  It is important to note that unlike activin, ACVR1B requires the presence of other coreceptor proteins like Cripto for its signaling activity.