Dead Cleaner Shrimp?

[Clown]

Well yesterday i picked up a new cleaner shrimp
Later that night i noticed that it was upside down,
And i wasnt sure if it was still living or what so i left in in there i woke up the next morning and it was gone nothing there at all,
all i have in the tank is 2 clowns and a sand sifter goby
so i picked one up today
and same thing but i found it on its side kinda tunked behind a rock
Are they dead or what?
My salinity is at .19 and all my levels are fine any ideas?