okay, what type of bug did I get with my order?

[justinl]

only the active fast swimming isopods are fast active swimmers. Isopoda is a very broad family which is comprised of mostly herbivores and detritivores; not all of them swim. only a handful are the dreaded parasites we are all familiar with.

OP, you say they are saucer shaped. I assume you mean top to bottom like a pancake? The fact that you mention that they have articulated segments like a pillbug says isopod to me (amphipods generally look squished side to side). If you are paranoid about parasites, chuck it. It's very likely harmless though.