The scientific name assigned to the order of gastropods commonly known as sea slugs or sea slugs is nudibranchs (Nudibranchia), which means "bare-gilled." This characteristic is evident in the external shape of the new species of sea slug discovered, although it may seem strange due to the distance, almost simultaneously in the waters of the coast of England and the Gulf of Cádiz. In addition to the gills located outside the body, this new species (new to science, it can be assumed that it has existed for millions of years) has a morphology that can also be considered strange, at least to the eyes of humans not accustomed to observing these shellless mollusks that live on the seabed.
The first studies on the specimens captured in scientific expeditions on the English coast (2018 and 2019) and in Cádiz (2020) suggested that they were varieties of the already known species Pleurobranchaea meckeli, a relatively common slug in the eastern Atlantic and the Mediterranean and similar to the spotted slug (P. maculata). In fact, the experts from the Center for Environment, Fisheries and Aquaculture Sciences of the United Kingdom and the Spanish Institute of Oceanography (IEO-CSIC) who participated in this research selected, from among the multiple specimens of marine animals collected with nets, trawling in both locations (southern England and the Gulf of Cadiz), a collection of 24 sea slug specimens that were considered to belong to three species.
After analyzing the slugs in detail and applying DNA analysis, the experts came to the conclusion that 14 of the specimens studied belong to what should be considered a new species. Based on the family to which they belong and the location of the first specimens, the authors have proposed the scientific name of Pleurobranchaea britannica. The authors indicate that although up to now only specimens of this species have been located in the waters of southern England and Cádiz, "we hypothesize that it could probably be distributed along the entire Atlantic coast of Spain, Portugal and France up to the approaches southwest to the English Channel".
The first signatory of the scientific article in which the results are presented, published in the journal Zoosystematics and Evolution (January 2024), are the researchers Martina Turani and Leila Armona, from the University of Bergen (Norway), while in the final position Among the signatures is Juan Lucas Cervera, professor at the University of Cádiz and researcher at the Marine Research Institute (INMAR).
The specimens studied measure about 2 centimeters long and the scientific description of the external shape of the new species is certainly detailed (transcription of the scientific article, unofficial translation):
"Species with a large oval body and a mantle formed by irregular polygons delimited by shallow grooves. The color of the body is translucent, sometimes with a fine pigmentation that ranges from cream to ocher, and with opaque white spots distributed irregularly throughout "the mantle, the oral veil, the gills and the back part of the foot, which is rounded and is not covered by the mantle. The internal viscera are visible due to transparency in light-colored specimens."
The scientific description, which is accompanied by several images (at the bottom) continues in these terms: "The rhinophores [organs in which the receptors for odors or flavors are located] are smooth and have a dark brown anterior part, while the posterior part is densely covered with white spots. The eyes are visible at the outer base of the rhinophores. The oral velum is trapezoidal and fuses with the mantle at the insertion of the rhinophores. The anterior edge of the oral velum is slightly irregular."
"Some specimens have a series of white spots in the corners of the veil. The gills, located on the right side of the body, are clearly visible as they are not covered by the mantle, they have the same color as the body and are bipinnate, with between "15 and 18 pairs of pinnules and a smooth rachis. It almost always has white spots, of variable density, visible on the rachis and gill pinnules."
"The genital openings are located in front of the gill and the nephropore is clearly visible, as it is covered by a circular fleshy papilla, which may also have white dots. The anus is located above and between the sixth and seventh pinule of the gill "The foot has no grandula pedia and the sole is not smooth, but has a certain pattern."
In the image above, A. Complete radula B. Lateral teeth of the radula; C.View from above of the anterior part of the mandible D.Lateral view of the anterior part of the mandible
