Carronella pellucida

Carronella pellucida (Alder & Hancock, 1843)

Taxonomic note: The classification of the Flabellinidae had remained fairly stable until in 2017 a series of works appeared (Furfaro et al., 2017; Korshunova et al., 2017) that intended to clarify the status of the Flabellinidae family. The main objective of the paper by Furfaro et al. was to molecularly characterize the Mediterranean species while the paper by Korshunova et al. wanted to delve into the phylogenetic relationships between various members of the Flabellinidae family and the other families of aeolidaceans.
Both works were based on the combination of molecular and morphological techniques and, in fact, do not offer very different results, but differ on the size and origin of the studied samples and, mainly, on the interpretation of the results. After the appearance of the paper by Furfaro et al., many Mediterranean species of the genera Calmella, Flabellina and Piseinotecus were grouped under the common genusFlabellina, but had certain problems with some species that did not fit well with the proposed classification (e.g,Flabellina babai) , discovered that the Mediterranean and Atlantic populations ofFlabellina ischitana correspond to two different cryptic species, and noted the problems of the cryptic group formed by Calmella cavolini / Flabellina confusa / Piseinotecus gaditanus, indicating the need for further studies to clarify their status.
Curiously, these studies were being carried out practically in parallel by the group of Korshunova et al. but on a much wider sample of species that included specimens from the Arctic, North Atlantic, Pacific and Indian Oceans. This second paper confirms the polyphily of the family Flabellinidae, but the interpretation of these results becomes a real revolution for the taxonomy of the aeolidaceans, especially for the family Flabellinidae.
Both papers show that there are two well differentiated clades (groups) in the Flabellinidae: species like Coryphella pedata and similars, with cerata that come directly from the back, and species like Flabellina affinis and similars, with cerata of each group coming from a stalk or pod. Although Furfaro et al. consider the species of both clades belonging to the genusFlabellina within the family Flabellinidae, Korshunova et al. distinguishes two families: Coryphellidae and Flabellinidae sensu stricto, also creating many different genera in these families to include the species they study. Its taxonomic proposal, curiously, solves the problems found by Furfaro et al.
In a way, both papers complement to each other, although in the paper by Korshunova et al. it is evident the lack of studies on tropical flabellinid species and those from southern America and Africa, so the subject has not been settled. The proposal to create new genera to collect small groups of species, instead of multispecific genera, seems to be the trend in some of the phylogenetic works of recent years. A detailed discussion of this exciting controversy can be found at (https://opistobranquis.info/en/flabellinidae/).

• Flabellina pellucida (Alder & Hancock, 1843)
• Coryphella pellucida (Alder & Hancock, 1843)
• Coryphella rutila Verrill, 1879
• Eolis pellucida Alder & Hancock, 1843 (original)

Description
It can reach a size of up to 40 mm. The base color of the body is hyaline white. The oral tentacles and rhinophores have the distal end coloured opaque white. The rhinophores are smooth. There are numerous cerata gathered in 6-7 groups on each side of the back, the first two well defined and grouping up to about 20 cerata. These are long and thin, hyaline and with the brown or reddish digestive gland visible inside; The apical end of the cerata is opaque white. The foot has a pair of thin and curved propodial tentacles on its front end.

Biology
It lives on rocky substrates and on submerged lines, on the hydrarian colonies it feeds on. Its food are the polyps of different hydrarian species from the genera Tubularia, Eudendrium, Hydrallmania and Kirchenpaueria.

Etymology

• Carronella. After Loch Carron, a sea loch on the west of the Scottish Highlands, where numerous specimens  of Eolis pellucida have been observed over many years.
• Pellucida. From Latin “pellūcida”, transparent.

Distribution
It is an amfiatlantic species, cited both in northern Europe (from southern Ireland and England to Norway and Russia) and on the Atlantic coasts of Canada, United States (Maine and Massachusetts) and Greenland. The only Mediterranean report corresponds to Ros (1975) who cites it in Blanes, Spain, but it has not been seen again, despite the intense and continuous surveys carried out all along the Iberian shores.

Known georeferenced records of the species: Carronella pellucida

Sources:
OBIS GROC 2010-2011 Enric Madrenas João Pedro Silva Bernard Picton GBIF	OPK VIMAR Manuel Ballesteros M@re Nostrum Altres fonts Marine Regions

Similar species
Carronella enne, a deep-water species native to the North Atlantic, very similar to C. pellucida from which it is separated only by molecular analysis.

More pictures

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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

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