The present invention relates to an anchor configured for minimally-invasive implantation and sized to remain securely positioned within at least a portion of the gastrointestinal tract of an animal. The anchor includes a radial spring formed from an elongated resilient member shaped into an annular wave pattern about a central axis. The anchor defines a central lumen and provides an outward radial force, while allowing for substantial flexure about its perimeter. The anchor is generally removable, but can include fasteners, such as barbs, to further secure it to the surrounding anatomy. In some embodiments, the anchor includes a connector coupling a fixed portion to a removable portion. Further, the anchor can be used to secure a medical device within the body, such as a flexible sleeve within the intestine.