I can't tell you about it's care, but I believe you may have mealy bugs.

Planto

yikes! thank you planto. i have removed the plant from the planter, sprayed everyone down with neem and replanted some of the healthy cuttings of the muscosa in a new pot, after blasting it with water and then neeming it. thank you...

Sure thing. Just keep an eye on your neighboring plants (the plants that were near your Crassula) as they do have the tendency to spread. I don't know much about treating them (Sorry...), my Mother purchased a Sansevieria online last year that had them (didn't know it at the time), and they spread to all but one of her other Sansevierias. We didn't see any on the other Sans at first, I eyeballed them really well in fact while throwing away the culprit, but in a matter of weeks, the others were infested (I wasn't looking at them daily). I know we could have treated them, but as heavily infested as they were and how tight some of those Sansevieria leaves grow, my Mother just wanted to cut her losses.

Planto