A gastrointestinal barrier implant including a support, a distal barrier tube extending from the support in a first direction, and a proximal retainer extending from the support in a direction opposite to said first direction, wherein the proximal retainer is adapted to be anchored to an internal wall of the stomach of a user and to extend from the stomach through the pyloric orifice such that the support is located below the pyloric orifice, the support depending from the proximal retainer, and wherein the distal barrier tube depends from the support so as to provide a liner through the duodenum. A surgical anchor suitable for fastening an implant to body tissues in vivo, the anchor comprising a mounting head and a pair of legs extending from the mounting head, distal end portions of the pair of legs remote from the mounting head being adapted to pierce the implant and body tissues, the mounting head being engageable by a coupling device for deploying and retrieving the anchor in use, the pair of legs being movable relative to the mounting head between a piercing configuration assumed by the legs at a first temperature in which the distal ends of the legs are mutually positioned to pierce the implant and tissues for installation of the anchor, and an anchoring configuration assumed by the legs at a higher temperature in which the distal ends of the legs are displaced away from the piercing configuration for securing the implant and tissues in use. A tool for delivering and placing a surgical anchor, comprising a handle carrying a flexible filament of a length to enable its endoscopic introduction to the zone in which the anchor is to be placed, the filament comprising a sheath and a flexible core displaceable longitudinally within the sheath, means carried by the handle and actuable for displacing the core relative to the sheath, the core having at a distal end a coupling device for releasably engaging a head of the surgical anchor, and the sheath having at a dista
