Cuttlebone

Cuttle fish bone is a great source of calcium for isopods and they go crazy for it! It is soft enough for them to eat as a whole so you don't have to worry about shaving it or making it into a powder. Once they eat the "meat" of it and leave the little flat shell behind, just toss it out and replace it with a new one.

These are nice pieces of cuttlebone. They're about 3-4" long and rather thick.