the baby sea star is probably a micro brittle and thats a great thing. they are detritivores and are an excellent addition to your clean up crew if you see one there are dozen you're not seeing.
or they could be an asterina star which is generally a good thing (only about 1 in one hundred species are a problem, the problem species are RARE but they do occur) if your not seeing a problem with your zoanthids then dont worry your most likley in the clear.
if your seeng baby snails chances are they might be strombus maculatus google images them, and they are another great addition as they are a great small algae grazer
or they may be pyramidellid snails which is not good but they mostly stay towards other snails and bivalves as they need to dine in a parasitic manner to survive. if your seeing the baby snails attached to Large snails near the foot, its a problem.
