Answer: Ixodes species tick (fragment), unengorged female
As Blaine, Idzi, Sheldon, Florida Fan, Richard, Agnes, and William nicely described, we can easily identify this tick fragment as an Ixodes species by its characteristic 'U-shaped' anal groove. Lack of festoons also supports the identification. One of our tick experts, Ellen, mentioned that the color is a good feature for determining sex, since female Ixodes are orange-brown while males are black and nymphs are transparent charcoal-grayish. Color can also be helpful for determining the degree of engorgement since adult females will become grayish-white once becoming engorged due to growth of new opisthosoma tissue. Thanks for the great description Ellen!