Not worried about these critters...just not sure what they are. You will have to zoom in on the feather duster looking thing as it is quite small and has been for almost a year. The other is a mushroom looking thing that moves around quite a bit on the rock, sand or whatever.
The first makes me think Stomatella snail (the eyes hiding in the shade?) Or a very extended odd looking limpet but id bet on #1. The second pic I'm not sure what I'm looking for but I don't see any pests.