Calla palustris - rhizome
Zantedeschia (aka Calla) - corm The ones with the spotty leaves and coloured flowers.

I disagree :-) Callas are aroids and the root structure of any aroid is a rhizome.

It is sometimes pretty easy to confuse the two terms and they are often used interchangeably. The difference is that corms have a papery tunic - rhizomes do not - and corms reproduce or develop cormlets whereas rhizomes just spread or enlarge. They can be cut or broken into chunks for propagation.

Thanks for the info guys, I appreciate it. Just for clarity, I was referring to Zantedeschia.