Geomulticast is a specialized location-dependent multicasting technique, where messages are multicast to some specific user groups within a specific zone. In this paper, we propose architectures and protocols for supporting geomulticast services in a cost effective way and with high message delivery accuracy in the challenging environment of mobile ad hoc wireless networks. Since in mobile ad hoc networks there is no fixed infrastructure as in cellular networks we use mobility-based clustering to cluster the various mobile nodes. Using this clustering approach as the basis, we describe several geomulticast zone formulation and representation methods that present trade offs between accuracy, simplicity and cost effectiveness. Moreover, we propose a direction guided routing (DGR) protocol which creates cluster-head based limited mesh structure within a guided region, in order to deliver packets with reliability and reduced overhead to the final destinations. Two geomulticast membership management strategies which depend on geolocation storage position are also presented and investigated. Finally, we define and formulate a framework in order to evaluate the performance of the design alternatives used for the support of geomulticast services in mobile ad hoc networks. Based on this framework we evaluate the performance of the proposed architectures and protocols, and we, obtain some insight about the impact of the various design and operational parameters on the overall system performance.