The tiny sea slug is very similar to the more well-known four-lined nudibranch Polycera quadrilineata – and it's almost impossible to tell the two species apart when underwater.

The new species is presented in a scientific paper by Cecilie Gotaas Sørensen, Cessa Rauch, Marta Pola, and Manuel António E. Malaquias, who have been working on the project «Nudibranchs of Southern Norway» for the last few years.

Found on the west coast

Polycera norvegica appears in two main morphotypes, one with yellow/orange pigmentation and one with tiny brownish specks or dots. The former is very similar to P. quadrilineata, but the dotted variety should be possible to distinguish.

The new species has been found in numerous locations from Egersund to Trøndelag on the Norwegian west coast, and we wouldn't be surprised if it turns out to have an even wider distribution. Perhaps it can be found in the same areas as Polycera quadrilineata.





Very similar – but not sisters

Even though the two mentioned species are very similar, they are not true sisters. The paper reveals that the new species is more closely related to Polycera faeroensis according to DNA analysis.

Polycera quadrilineata was described by O. F. Müller back in 1776, after having found it in Drøbak in the Oslo fjord. After over 240 years, one of the most common nudibranchs of the North-East Atlantic has a new family member.

Read the article here

The scientific paper is called «Integrative taxonomy reveals a cryptic species of the nudibranch genus Polycera (Polyceridae) in European waters» and was published in the Journal of the Marine Biological Association of the United Kingdom.