Diatoms were examined from the skin of a male sperm whale (Physeter macrocephalus L.) stranded on the Belgian shore in 1994 on its return from the northem Atlantic to more southern latitudes. The morphology (LM and SEM) and taxonomy of the three ceticolous taxa present are discussed. Epiphalaina aleutica Holmes, Nagasawa & Takano var. aleutica was the most abundant species in the material. T. staurolineata Denys spec. nov., separated from T. olympica (Hust.) Holmes,Nagasawa & Takano after examination of type material of the latter, was only slightly less numerous. Tursiocola omurai (Nemoto) Denys nov. comb. occurred only sparingly. In addition, Epiphalaina aleutica var. lineata Denys var. nov., is described from material collected previously on a Dall's porpoise from the northern Pacific.