Aidamochelia claustracola, gen. et sp. nov., an endocommensal amphipod, is described from two hexactinellid sponges, Aphrocallistes beatrix and Hertwigia falcifera, from deep coral bioherms off Florida's east coast. Aidamochelia claustracola is the third genus and fifth species described from one of the rarest gammaridean amphipod families, the Didymocheliidae. Aidamochelia claustracola is separated from the two other genera, Didymochelia and Apodidymochelia, in having expanded bases on pereopods five through seven and a biramous third uropod. Observations of live specimens of Aidamochelia claustracola in the host sponges show them to occur as male- female pairs and to have eyes consisting of a triangular ommatidial mass that fades on fixation. Scanning electron microscopy and light microscopy studies of siliceous spicules found in the mouthpart field and gut indicate that Aidamochelia claustracola may feed on tissue of its hosts. This species represents only the second record of the family from the Northern Hemisphere and extends the known range of the family to the western Atlantic Ocean.