What is the difference between ostia and osculum?

Osculum: A large opening in a sponge through water flows out of the sponge. the sponge may have more than one Osculum.

Ostia: A series of tiny pores all over the body of a sponge that let water into the sponge. One of these is called Ostium. 

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Wetlands form where water and land meet. a lake with a wetland fringe can fill in with decayed plant and animal material to become a wet meadow. a pond can fill in to become a bog or fen. sediment can fill in a river marsh to become a swamp.flooding of coastal lowlands from rising sea levels has created broad coastal marshes that are protected from wave action by barrier islands or reefs. coastal wetlands also form when rivers deposit sediment as they reach the ocean. plants then take root and hold the soil firm against the forces of tides and waves.