molting?

First time poster here & new to the hobby of saltwater aquariums. So far, all has been well.. I’m curious as to what these little red leg hermit crabs are up to if anyone could shed some light? When I approached the tank my Nassarius snails were circling the pair of hermit crabs as if...

So just got back home and I come home to this… my shrimp molted just a few days ago which is why I’m confused and it’s acting strange it’s just on the sand twitching and trying to swim my fish and other inverts look normal… any suggestions?