First occurrence of the genus Pleurobranchaea Leue, 1813 (Pleurobranchida, Nudipleura, Heterobranchia) in British waters, with the description of a new species

In the north-eastern Atlantic and Mediterranean Sea, the pleurobranchid genus Pleurobranchaea Leue, 1813 is represented by two species, Pleurobranchaea meckeli (Blainville, 1825) and Pleurobranchaea morosa (Bergh, 1892). The former is a well-known species distributed from northern Spain to Senegal and the Mediterranean Sea, while the second is a poorly-described species. In this contribution, species delimitation analyses (ABGD and COI/16S p-distances) identified a third undescribed Pleurobranchaea species from samples collected in south-western UK waters and the Gulf of Cadiz (SW Spain). This new species, Pleurobranchaea britannica sp. nov., is also supported by several morphological synapomorphies. The British specimens constitute the first occurrence of the genus Pleurobranchaea in UK waters.