For commercial development of a European scallop culture industry based on natural collection of seed, a method of predicting time and location of peak spatfalls is essential. Planktonic identification of scallop larvae using light microscopy, which would allow development of such a prediction technique, has been deemed impossible. Researchers have instead focused on the use of scanning electron microscopy of the hinge structure or development of biotechnological methods to resolve the difficult identification in plankton samples. This study presents details of morphological characteristics, excluding ultrastructural traits of the hinge, that have been used to identify king scallops, Pecten maximus, larvae during their planktonic phase in Mulroy Bay, Ireland over the last 26 years. The most useful features for identification of king scallop larvae in natural plankton samples were the pointed anterior end, the indistinct umbo, the pale color and the length–height relationship. These characteristics for identification of king scallop larvae in natural plankton samples have led to development of a technique for prediction of time and location of scallop spatfall and commercial collection of scallop spat at intensities exceeding 3000 spat per collector bag.