Flabellinidae

Flabellinidae Bergh, 1889

The family Flabellinidae groups together a group of nudibranchs belonging to the suborder Aeolidida, characterized by their elongated body, the presence of numerous cerata arranged in dorsolateral rows, and a frequently bright coloration. They are distributed in temperate and tropical seas around the world, where they inhabit rocky bottoms, reefs and areas with an abundance of hydrozoans, their main source of food.

Flabellina affinis by Miquel Pontes by Pontes, Miquel

Diagnostic characters

The flabellinids share a series of morphological characteristics that allow them to be differentiated from other families of aeolids:

• Body narrow and elongated.
• Oral tentacles very long, with well-developed propodial tentacles.
• Rhinophores generally smooth or bearing annular papillae, not branched, with a chemoreceptive function.
• Numerous cerata, slender and elongated, arranged individually or in groups on peduncles distributed along the dorsolateral region.
• Intraceratal digestive gland with branches visible through the semitransparent epidermis of the cerata.
• Anus generally pleuroproctic.
• Simultaneous hermaphroditic reproduction, with genital structures located on the right side of the body.
• Jaws present, with a triseriate radula.
• Bright coloration, often iridescent, presumably aposematic.
• Highly active, feed on athecate hydroids.

Taxonomy

For decades, the genus Flabellina was considered a “catch-all” taxon, which included numerous species of aeolids with dorsolateral cerata and striking colorations. However, recent research has shown that this genus was paraphyletic (Korshunova et al., 2017). Thanks to the combined use of detailed morphological data and analysis of mitochondrial and nuclear genes (such as COI, 16S and H3), the family Flabellinidae sensu stricto has been delimited, separating numerous genera that were previously included in Flabellina.

This change led to a profound revision of the systematics of aeolids, dividing the old clade Flabellinidae “sensu lato” into several families, including Samlidae, Coryphellidae, Paracoryphellidae and the redefined Flabellinidae.

It should be noted that there are still controversies about the validity of some new genera and the stability of the diagnostic characters used. However, molecular phylogeny has proven to be a key tool to clarify the evolutionary relationships within this highly diversified group.

The following genera are currently recognized as valid within this family (Korshunova et al., 2017; Korshunova & Martynov, 2020):

Flabellinidae Bergh, 1889

• Calmella Eliot, 1906
• Carronella Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, H. Saito, Lundin, Schrödl & Picton, 2017
• Coryphellina O’Donoghue, 1929
• Edmundsella Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, H. Saito, Lundin, Schrödl & Picton, 2017
• Flabellina McMurtrie, 1831
• Paraflabellina Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, H. Saito, Lundin, Schrödl & Picton, 2017

The Mediterranean and near-Atlantic species included in this family are:

Calmella cavolini

Calmella gaditana

Carronella pellucida

Coryphellina rubrolineata

Edmundsella pedata

Flabellina affinis

Flabellina dushia

Paraflabellina gabinierei

Paraflabellina ischitana

Referencias

• Korshunova, T., Martynov, A., Bakken, T., Evertsen, J., Fletcher, K., Mudianta, W., Saito, H., Lundin, K., Schrödl, M., & Picton, B. (2017). Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: Aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda). ZooKeys, 717, 1–139. https://doi.org/10.3897/zookeys.717.21885
• Korshunova, T., & Martynov, A. (2020). External diversity is correlated with internal variability: hidden taxonomic diversity and complex evolution in aeolidacean nudibranchs (Mollusca: Gastropoda). Contributions to Zoology, 89(1), 71–120. https://doi.org/10.1163/18759866-BJA10003

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