Could have a critical role in early developmental decisions in the sea urchin embryo. Homodimer; disulfide-linked. Highest levels of expression in the egg and prehatching blastula. During late cleavage stages, it accumulates progressively to a circumequatorial band. During gastrulation it is detected primarily in the presumptive foregut and ciliated band. By pluteus stage, it is detected only in these cell types. Belongs to the TGF-beta family.