Nemesignis banyulensis

Nemesignis banyulensis (Portmann & Sandmeier, 1960)

Nemesignis banyulensis by Enric Madrenas

Taxonomic note: Furfaro & Mariottini (2021) published “Integrative taxonomy is an evolving field of multidisciplinary studies often utilised to elucidate phylogenetic reconstructions that were poorly understood in the past. The systematics of many taxa have been resolved by combining data from different research approaches, i.e., molecular, ecological, behavioural, morphological and chemical. Regarding molecular analysis, there is currently a search for new genetic markers that could be diagnostic at different taxonomic levels and that can be added to the canonical ones. In marine Heterobranchia, the most widely used mitochondrial markers, COI and 16S, are usually analysed by comparing the primary sequence. The 16S rRNA molecule can be folded into a 2D secondary structure that has been poorly exploited in the past study of heterobranchs, despite 2D molecular analyses being sources of possible diagnostic characters. Comparison of the results from the phylogenetic analyses of a concatenated dataset (the nuclear H3 and the mitochondrial COI and 16S markers) and from the 2D folding structure analyses of the 16S rRNA from the type species of the genera investigated demonstrated the diagnostic power of this RNA molecule to reveal the systematics of four genera belonging to the family Myrrhinidae (Gastropoda, Heterobranchia). The “molecular morphological” approach to the 16S rRNA revealed to be a powerful tool to delimit at both species and genus taxonomic levels and to be a useful way of recovering information that is usually lost in phylogenetic analyses.” While the validity of the genera Godiva, Hermissenda, Nanuca and Phyllodesmium are confirmed, a new genus was necessary and introduced for existing Dondice banyulensis: Nemesignis.

Synonyms

• Dondice nicolae Vicente, 1967
• Godiva banyulensis Portmann & Sandmeier, 1960
• Dondice banyulensis (Portmann & Sandmeier, 1960)

Description
It is the largest aeolidacean of the Mediterranean as it can reach up to 7 cm in length. Unmistakable by its size and by its spectacular orange color, darker on the head and lighter on the back, where the internal organs can be guessed by transparency. All the animal’s body is traversed by a white dorsal midline passing between the base of the rhinophores, running all along the head and bifurcates to penetrate in the inner side of the oral tentacles. There is another white line that runs along both sides of the body, below the insertion of the cerata. Sometimes there is also a white dashed line between the bases of cerata groups. The oral tentacles are very long, very wide at the base and colored orange except at the tip, which is white. The rhinophores are thin and short in relation to the size of the animal, they are almost completely ringed and coloured orange except the apex which is usually white. The cerata are usually assembled into 6 groups on each side of the body, each group with several rows of cerata. The cerata are long, slender, slightly curved and coloured orange, like the rest of the body. The digestive gland inside the cerata is shaped like a strand of brown. The anterior side of cerata may be iridescent white. The foot is very wide and semi-transparent, with all its margin tinged with an iridescent white line that runs all along it. At the tail, this marginal white line of the foot is fused to the dorsal white line. The propodial tentacles are thick and orange, but their tip is iridiscent white.

Biology
It is incomprehensible that the most spectacular and largest species of Mediterranean aeolidacean went unnoticed until 1960, when it was described by Portmann and Sandmeier as new to science. It is a very active species and, as most facelinids, when provoked extends its cerata sideways in a clearly defensive manoeuvre. It is found in a variety of habitats and substrates such as over hydrozoans colonies of the genus Eudendrium, on gorgonians (Eunicella verrucosa), in the coralligenous, wandering on sandy bottoms or on rocky walls with photophilic algae. This species has been reported feeding on polyps Eudendrium, polychaetes and even other aeolidacean nudibranchs (Flabellina pedata, F. affinis, Cratena peregrina or Facelina rubrovittata). It has been observed that mating animals vigorously move their cerata. The spawn is a heavily scalloped lace with white eggs.

Etymology

• Nemesignis, from the union of the Greek word Nemesis, that recalls the homonymous Greek goddess and her role of compensatory justice, with the Latin word Ignis, that is the fire that burns and blazes, linked to the fiery red colour of the type species of the genus.
• Banyulensis referred the oceanographic station of Banyuls-sur-mer (France)

Distribution
Until a few years ago, N. banyulensis was considered to be restricted to the western Mediterranean. However, it has recently been reported along the coasts of Croatia and Turkey, and in recent years it is known to be present on the Iberian Atlantic coast, from Tarifa (Cádiz) to Pasaia (Basque Country) and the Canary Islands. In the Iberian Peninsula it inhabits all the coastal areas of the Mediterranean and the Balearic Islands. In Catalonia it has been reported in many locations along the Costa Brava (Port de la Selva, Cadaqués, L’Estartit, Begur, Palamós, Tossa de Mar and Blanes) as well as off the port of Tarragona.

Similar species
Fjordia lineata, whitish and translucent body, not orange, smaller size, cerata with an anterior white line, oral tentacles shorter than rhinophores.

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More pictures

Bibliography

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Bibliography based on the works by Steve Long, 2006. Bibliography of Opisthobranchia 1554-2000 and Gary McDonald, 2009. Bibliographia Nudibranchia, with later updates from other resources.

Further reading

• AsturNatura
• Biodiversity Heritage Library
• CIB - Club Immersio Biologia
• DORIS
• El Litoral de Granada
• Flickr pictures
• GROC
• Interim Register of Marine and Nonmarine Genera
• M@re Nostrum
• NCBI GenBank
• OBIS - Search by Taxon
• Sea Slug Forum
• World Register of Marine Species

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