[Van down by the river]

Sorry about the mis-ID
The picture helps Thank you
What you are talking about is :
Calcinus elegans
1.8cm Carapace
Indo Pacific
intertidal to 10m
I haven't personally kept this one so I can only give a general idea.
It seems to be omitted from Sprung's lists, but there are so many options I guess he can't list them all. There is a Hawaiian variety that has orange instead of blue, but I like the blue better.
The Calcinus family usually graze on short turf algae, possibly some macro as well. They are realatively short lived so I suggest to reduce possibly destructive "fights" over shells, add some extra shells of similiar size. As to aggresion don't forget ALL hermits are opportunists! besides who could turn down a helpless, juicy, overturned escargo?
As nice as they are you could get more blue legs for money.(and some snail replacements)
Good luck and let us know how they behave....