Abstract: A subsea riser mainfold system is disclosed for handling marine well fluids from multiple subsea wells and transmitting the well fluids through a marine production riser. The system includes a marine floor base template having a support structure and a manifold chamber supported thereon. Pile guides are connected to the template for fixing the template to the marine floor. The sealed manifold chamber hull is mounted on the template between the pile guides, enclosing manifold means for operatively connecting the subsea wells to the production riser. An improved structural spanning support member extends over the manifold chamber hull for receiving and supporting the marine production riser. This spanning member has an upper riser-receiving platform portion and structural spider arms connected between the platform production and the pile guides through the spanning member.