Researchers involved in the development of dexterous robotic hands agree that a mechatronics approach to hand design is the only way to generate new levels of functional capabilities. As reported by several authors, the problems relative to the single component or subsystem design must be solved within a general frame of compatibility and integrability. In this paper the virtual and physical prototyping of a three-fingered gripper designed to be mounted on an autonomous underwater vehicle (AUV) for underwater manipulation as well as sampling specimens is reported. In particular, an overall description of the gripper design is discussed, with special attention to the required actuation and tendon transmission system, its integration within the mechanical structure and the required control architecture. Different solutions for the joint configuration and the structure of the tendon network adopted for the transmission system are presented. The integrated design of the finger is reported and the motivations leading to this particular implementation are thoroughly addressed, taking into account both the mechanical constraints and the control requirements. The overall finger design is modular, so that other design solutions comprising multiple fingers (e.g. for in-hand manipulation purposes or realization of cage gripper) are easily achievable by adding further modules without increase the overall dimensions of the device. Virtual prototype results are finally provided and discussed to prove the gripper behaviour and capabilities.