Most sponge body plans are slight variations on a simple tube-within-a-tube design. which of the following is a key limitation of sponge body plans? sponges lack the specialized cell types needed to produce more complex body plans. the reliance on osmosis/diffusion requires a design that maximizes the surface area to volume ratio of the sponge. choanocytes must be protected from the hostile exterior environment. spongin cannot support heavy bodies.
