wet/dry

do i need a protien skimmer and a wet/dry and if so what is the difference? i have
55gl
prizm protien skimmer
4 power heads
4 yellow tangs
1 blue hippo tang
1 clown
2 cucumbers
2 starfish
20 scarlet crabs
3 emerald crabs
3 flamins scallops
candy cane
open brain
3 fether dusters
10 turbo snails
sorry probably a dumb question but i need to know
 
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