Blindsense or even blindsight (of the two, I like blindsense better for this, I think) is ok, but I like tremorsense even better. Tremorsense for aquatic creatures specifically includes vibrations in water per the SRD; blindsense for the shark seems like an extension of its keen scent.
It should certainly swallow Large and probably even Huge critters! Before hp needed to cut out, though, we should probably pick natural armor. +20 or so? What do we get advancing our other worms to Colossal?