Hi Stephen, If you are asking about specifically zoological symbionts, I can't think of any true examples of symbiosis, though there are a number of examples of commensal relationships, as well as parasitism. But two examples of symbiosis involving mollusks and other-than-animal symbionts are the symbiotic algae found in Tridacna, Corculum, and some opisthobranchs (sea slugs); and the symbiotic sulphur-fixing bacteria found in deep sea vent clams. Paul M.