Runcina avellana

Runcina avellana  Schmekel & Cappellato, 2001

Runcina avellana by Enric Madrenas




































Pseudoilbia avellana   (Schmekel & Cappellato, 2001)

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 744313).
Taxonomic note: In the description of the species by Schmekel & Capellato (2001), authors referred to a single anatomically studied specimen, 1.2 mm long when alive, as having a radular formula of 3 x 1.0.1, which is considered by the authors as the rudimentary radula of a juvenile. They found no internal shell nor could recover any gastric plates after treating the sample with NaOH. These features induced Ortea (2013) to propose the provisional inclusion of this species in the genus Pseudoilbia within the Ilbidae family, including species of the genus Ilbia Burn, 1963 and Pseudoilbia Miller & Rudman, 1968 with no gastric plates within their digestive tract and the second genus also without spinal tooth. Specimens studied by Araujo et al (2022) were characterized by features consistent with the original description of R. avellana (sensu Schmekel & Cappellato, 2001), like the shape of the body, presence of a round brownish mark on the centre of tail, general colour pattern, absence of gizzard plates and presence of gills, specimens collected at Roses (Spain) about 45 km from the type locality, and clustered in the phylogenetic analyses among species of the genus Runcina, questioning the assignment by Ortea (2013). Moreover, the lack of rachidian teeth in R. avellana reported by Schmekel & Cappellato (2001) might be an artefact since only one apparently juvenile specimen was studied by these authors. Unfortunately, Araujo et al (2022) were not successful on obtaining the radula for study so, in the meantime, at OPK we prefer to keep the species R.avellana within the genus Runcina until further studies of other specimens that may appear in future allow confirmation of the inclusion in one or another genus.


  • Pseudoilbia avellana Schmekel & Cappellato, 2001

This species is about 2 mm long and has a clearly elongated body. The anterior notum is somewhat narrower than the foot and does not have any cephalic lobes while the rear end has an oval contour. The foot has the same width as the notum except in the front, where it protrudes slightly at the sides of the head region, and the rear, where it forms a short, rounded tail. The coloration is uniform chocolate brown except the anterior and lateral regions of the head, some areas of the edge of notum, foot and tail, which are semitransparent and lighter coloured. The eyes are clearly visible and are located near the side edges of the head region, on the lighter coloured area. The edge of the foot has small brown spots along its length and the tail has a larger spot of the same color, shaped like an inverted “Y”. Schmekel & Capellato (2001) state that the specimens had a single rounded branchial leaf.

This little-known species are known to live in Posidonia oceanica rhizomes, like other species of the same genus, and it has also appeared among masses of algae like Codium vermilara (personal communication of E. Madrenas).


  • Runcina. The Latin word for carpenter’s plane, a tool used to smooth the surface of the wood.
  • Avellana. This is related to the city of Avellino (Campania, Italy) which was called “Abella” during the Roman domination, and was known for their hazel plantations, whose fruit was called “nux avellana”, Abella nut. The fruit of the hazel was also known in ancient Castilian as “avellina”. Refers to the chocolate brown colour of this opisthobranch’s body, similar to hazelnut.

To date, R. avellana was only known from the town of Banyuls-sur-mer on the French coast of the western Mediterranean, thanks to the collection of 3 live specimens of 1, 1.2 and 1.5 mm in length. The record of a specimen collected from algae in the Medes Islands (Catalonia, Costa Brava) means the second global cite for this species, followed by a few more samples obtained by our group at Roses Bay (Spain) that were used in the study by Araujo et al (2022).

Known georeferenced records of the species: Runcina avellana
: GROC 2010-2011
: Enric Madrenas
: João Pedro Silva
: Bernard Picton
: Manuel Ballesteros.
: M@re Nostrum
: Altres fonts
: Marine Regions


    Western Mediterranean: ★☆☆☆☆
    Eastern Mediterranean: ☆☆☆☆☆
    Atlantic Ocean: ☆☆☆☆☆

This chart displays the monthly observation probability for Runcina avellana based on our own records.

More pictures


    Araujo AK, Pola M, Malaquías MAE, et al. 2022. Molecular phylogeny of European Runcinida (Gastropoda,  Heterobranchia): the discover of an unexpected pool of complex species, with special reference to the case of Runcina coronata. Zoological Journal of the Linnean Society. XX:1–28.
    Ballesteros M, Madrenas E, Pontes M. 2016. Actualización del catálogo de los moluscos opistobranquios (Gastropoda: Heterobranchia) de las costas catalanas. Spira. 6:1–28.
    Ballesteros M, Madrenas E, Pontes M. 2023. OPK - Opistobranquis. Available from
    Correa M, Madrenas E, Riesgo A, et al. 2015. First molecular approach to the study of Mediterranean Runcina Forbes [in Forbes & Hanley], 1851 (Heterobranchia: Runcinacea).
    Long SJ. 2006. Bibliography of Opisthobranchia 1554-2000. Bayside Books & Press, Tustin, CA, U.S.A. 672p.
    McDonald G. 2009. Bibliographia Nudibranchia. 2nd Online Edition, Annotated. 1072 pp  Institute of Marine Sciences, University of California, Santa Cruz. Available from
    Schmekel L, Cappellato D. 2001. Contributions to the Runcinidae. I. Six new species of the genus Runcina (Opisthobranchia cephalaspidea) in the Mediterranean. Vie Et Milieu-Life and Environment. 51(3):141–160. Available from ://WOS:000171829500005.
    Templado J, Villanueva R. 2010. Checklist of Phylum Mollusca. pp. 148-198 In Coll, M., et al., 2010. The biodiversity of the Mediterranean Sea: estimates, patterns, and threats. PLoS ONE 5(8):36pp.
    WoRMS Editorial Board. 2023. World Register of Marine Species. WoRMS. Available from

    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

Cite this article as:

Ballesteros, M., Madrenas, E. & Pontes, M. (2023) "Runcina avellana" in OPK-Opistobranquis. Published: 19/09/2012. Accessed: 02/03/2024. Available at (

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