Answer: Earthworm, a segmented worm in the Annelida phylum. As Hans pointed out, it has rings around its body and a "saddle" (clitellum) which is a sac in which eggs are deposited.
Thank you to Florida Fan for sharing your earthworm story. Another reader also wrote in with a comment on how often earthworms are submitted to the laboratory. It's true! We get an earthworm submitted to our laboratory about once per week in the spring and summer months; (granted, we are a large reference lab and smaller labs probably don't see as many).
We've had several examples of annelids on this blog before:
Case 234 shows what an earthworm looks like on histologic sections (although sending intact worms to the microbiology lab is always preferred to sectioning them!)
and Case 254 is an example of medicinal leeches - another annelid.