X-cell disease in common dab (Limanda limanda L.) caused by Xcellia lamelliphila (Perkinsea)

Historically, this condition in dab has been known as ‘X-cell disease’ for several decades, the nature of the cells associated with the disease was unknown. It has now been established that the aetiological agent is closely related to Perkinsids. Morphologically similar X - cells have been reported in epidermal lesions in flatfish from North America and  Japan  as  well  as  causing  pseudobranchial  growths  (originally  referred  to  as  ‘tu-mours’) in gadoids, which comprise of parasitic cells in a connective tissue stroma.