Azadinium is a dinophycean genus capable of producing azaspiracids (AZAs), a recently discovered group of lipophilic phycotoxins causing human intoxication via mussel consumption. Although initially described from the North Sea, the genus currently consisting of four described species is probably distributed worldwide. Here we report on Azadinium from the Shetland Islands, which are located in the northernmost part of the North Sea and are largely influenced by the Atlantic Ocean. Two strains of Azadinium were isolated from a single water sample. One strain was identified as Azadinium spinosum based on morphology and sequence data and had an AZA cell quota of about 20 fg per cell, similar to all other described strains of the species. The toxin profile consisted of AZA-1 and AZA-2 in a 2.3:1 ratio and a yet undescribed AZA of 715 Da. The other strain represents a new species and is here described as Azadinium polongum sp. nov. Like A. spinosum, but different to Azadinium obesum and Azadinium poporum, A. polongum has an antapical spine. A. polongum differs from A. spinosum by an elongated shape of the pore plate (Po), and X-plate, the location of the ventral pore, and the absence of a distinct pyrenoid with starch sheath. Molecular analysis based on SSU, LSU, and ITS sequencing supported separation of A. polongum at the species level. Detailed LC–MS analysis showed that A. polongum does not produce any known AZAs in measureable amounts.