Pleurobranchaea britannica: A new species of Sea slug discovered in UK waters 

A new species of sea slug, named Pleurobranchaea britannica, has been discovered in the waters off the southwest coast of England. This is the first recorded instance of a sea slug from the Pleurobranchaea genus in UK waters. 

It is a type of side-gill sea slug and measures between two and five centimetres in length. Specimens were collected during routine fisheries surveys conducted by Centre for Environment, Fisheries and Aquaculture Science (CEFAS), and the Instituto Español de Oceanografía in 2018 and 2019 off southwest England and in the Gulf of Cadiz, southwest Spain. 

In view of the presence of the distinctive side-gill on the right side of the body, the specimen was tentatively identified as Pleurobranchaea meckeli, a well-known species of the Pleurobranchaea genus typically found in waters around northern Spain to Senegal and across the Mediterranean Sea. However, its identity remained uncertain because no previous records of the species in UK waters existed.  

Pleurobranchaea britannica has been classified as a standalone species by the experts based on examination of the DNA, and the identification of physical differences in the appearance and reproductive systems when compared to known species.  

Sea slugs are a type of shell-less marine mollusc. They are an extraordinarily diverse group of animals. Being at the top of the food chain and functioning as both predators and prey, they are essential to marine ecosystems. To protect themselves from predators, several species specialise in recycling parts of the animals they prey on. For instance, absorbing toxins from certain prey and secreting the poison into their own skin. Their sensitivity to environmental changes makes them valuable indicators of ecosystem health, helping scientists understand the impacts of climate change and human activities on marine habitats. 



  1. Turani M, et al 2024. First occurrence of the genus Pleurobranchaea Leue, 1813 (Pleurobranchida, Nudipleura, Heterobranchia) in British waters, with the description of a new species. Zoosystematics and Evolution 100(1): 49-59.  
  1. CEFAS 2024. News – New species of sea slug discovered in UK waters. Posted 1 March 2024. Available at 


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