AbstractThe Teredinidae possess specialised calcareous paddle-like structures, the pallets, which flank the siphons. The external segmentation/non-segmentation of the pallets is used as the main diagnostic character to distinguish between the Teredininae (non-segmented pallet line) and the Bankiinae (segmented pallet line). The internal segmentation of the pallets has, however, seldom been accessed. Therefore, in the present study, the internal structure of the pallets of Psiloteredo megotara (Teredininae) and Nototeredo norvagica (Bankiinae) was analysed using scanning electron microscopy. Pallets of P. megotara were segmented, in a fashion similar to those of N. norvagica, rather than lacking true segmentation as had been reported previously. This finding, affecting a key character state, supports results from previous molecular work and shows the need for further work to ascertain the valid compositions of the Teredininae and Bankiinae.