Detailed descriptions and illustrations are presented of the structure of three representative species of tropical shipworms, Nausitora hedleyi, Teredo furcifera and Teredora princesae. The disposition of the various organ systems is described and illustrated with notes on the histology of the different regions so as to throw light on the adaptations and specializations of these unusual bivalves. The trend of evolution within the Teredinidae is discussed in the light of the available evidence contained in the present morphological studies.