Mollusca
The phylum Mollusca is made up of the invertebrate organisms that we call mollusks. They are the largest marine phylum, making up 23% of all marine life, however there are also terrestrial mollusks as well. The phylum is extremely diverse and examples of these organisms could range from squids to snails. Most mollusks are snails or slugs. The basic definition of a mollusk is an organism that has a soft, bilaterally similar, and un-segemnted body with a shell on top.
Excretory System
Most mollusks have a basic excretory system. First, contaminants are filtered by a pair of nephridia, which are like kidneys. From there nitrogenous waste flows down canals to a bladder like sack. While there extra water is reabsorbed into the body. Then the remaining contaminants are expelled from the bladder through a pore on the outside of the body. With this there is also the excretion of feces from the end of the digestive system. Some lack a bladder and just dump waste straight from the nephridia straight out of the body. An interesting side note is that some mollusks use their waste products to actually build their shells and stay afloat.
Examples
A snail (Gastropoda) is probably one of the best known examples of a mollusk. Their excretory systems are capable of fully processing waste and excreting it as urine and feces.
A squid (Teuthida) is another example of a mollusk. Contaminants are removed from the body and sent to the bladder. From there the pulsing of the blood stream causes the bladder to expand and contract, allowing waste materiel to leave the body.
One more example of a mollusk is the giant clam (Tridacna gigas). In a giant clam the nephridia take contaminants and sends them to the bladder. From the bladder the contaminants are simply released at the from of the body where the current of water exiting the body flushes it out.