Hi, just a couple of observations...
shell replacement seems to be tied to the moons activity... I know from discussing with friends in England, that ALL our crustys do it at the same time... give or take a day... mine all shed on sunday!
Hermits do NOT only shed the exoskeleton from their legs... it's just much thinner over their bodies, and as such the first thing that gets eaten in the tank... normally by the hermit itself, as it desperately tries to replace the lost calcium in its own body!
That 1/2" non-snail sounds like a nudibraich... (sea slug) Nudis normally eat food the same colour as them, so If it's green, then it's probably an algae-eater... if it's pink and spiky then it's "look out star polyps"... do a google on sea slugs to see just how many it looks like!
they don't have a long lifespan, so don't bother naming it, unless it's after your least favourite politician or an ex-partner!