Knoutsodonta pictoni

Knoutsodonta pictoni  Furfaro & Trainito, 2017

Atalodoris pictoni @ Costa Brava, Spain by Enric Madrenas













































Atalodoris pictoni   (Furfaro & Trainito, 2017)

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 1565334).
Taxonomic Note: This recently described species has been identified repeatedly as Onchidoris pusilla (Alder & Hancock, 1845) because of its similar morphology: dark brown body due to scores of the same color and completely white rhinophores. However, the gill leaves in K. pictoni are of the same color as the body, in contrast to the white gill of the original description and the other reports of true O. pusilla. Hallas & Gosliner (2015) in their study on the phylogeny of the Onchidoridae establish the new genus Knoutsodonta Hallas & Gosliner, 2015 where they include several Onchidoris species (brasiliensis, depressa, jannae and oblonga) lacking a medial tooth in their radula. In the article describing K. pictoni, Furfaro & Trainito (2017) extend to 16 the number of known species of the genus Knoutsodonta, of which 6 are species living in the Mediterranean (K. pictoni, K. albonigra, K. bouvieri , K. depressa, K. neapolitana and K. sparsa).

Animals of this species may reach up to 13 mm in length, but they do not usually exceed a size of 9-10 mm. The body shape is almost circular and it has a very dark brown color, formed by almost continuous spots of the same color. There are whitish spots near the edge of the mantle. Under the mantle the typical spiculation of the genus Onchidoris can be seen by transparency. The dorsum has slightly conical elevated and well spaced tubercles. The tubercles at the edge of the mantle are smaller. The tubercles have whitish the base and brown the apex. The rhinophores are completely white and retractile; have rudimentary lamellae, up to 10 in the largest specimens. The rhinophoral sheath is not high and has two large tubercles, one antero-internal and one lateral. The gill is formed by up to 9-10 bipinnate leaves in the largest specimens; the gill leaves are arranged in a circle around the anus, they are not retractile, they are semitransparent but they have numerous brown spots that give them a dark color. The intrabranchial circle has three tubercles, two anterior and one posterior, which closes the circle of gill leaves. The foot is whitish but has tiny brownish-red spots, visible with a binocular microscope, and a reddish-brown stain corresponding to the internal viscera. There are also brown spots on the flanks of the body and on the back of the foot. The mouth is located at the center of a sort of oral veil that extends laterally.

Specimens of this species were known in different points of the Catalan Costa Brava (Spain) since 1992 but were erroneously assigned to the species Onchidoris pusilla. It lives under rocks and almost always on colonies of encrusting bryozoans such as Reptadeonella violacea (see Furfaro & Trainito, 2017) on which it is usually unnoticed due to its color similarity. The predated areas of the bryozoan colony appear whitish, making it easier to tell if the nudibranch is around or not. The spawn, which is usually laid on top of the bryozoan briozoo, is formed by a semitransparent cord wrapped in a tight circular spiral of up to 7 turns, with numerous white eggs. It has been reported how two animals can lay a complex pattern in which one egg spiral is completely enclosed within another. Eggs are usually laid from April to May.


  • Knoutsodonta, from the Greek meaning “lame tooth”, to represent nudibranch species that lack a rachidian or middle tooth.
  • Pictoni. After Bernard Picton, eminent British specialist in opistobranchs of the North Atlantic.

K. pictoni has an Atlantic-Mediterranean distribution and has only been found so far on the Scottish and Irish coasts and in the central and western Mediterranean (see Furfaro & Trainito, 2017). In the Iberian Peninsula there are only reliable reports from the Costa Brava (Port Lligat to Lloret de Mar), and from the Maresme, where it has been reported in Llavaneres (Ballesteros et al., 2016), in all cases cited as O. pusilla or Knoutsodonta sp.

Known georeferenced records of the species: Knoutsodonta pictoni
: 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 Knoutsodonta pictoni based on our own records.

More pictures


    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
    Ballesteros M, Pontes M, Madrenas E. 2019. Els nudibranquis del mar català. Figueres: Brau Edicions. 192 p.
    Betti F, Bava S, Cattaneo-Vietti R. 2017. Composition and seasonality of a heterobranch assemblage in a sublittoral, unconsolidated, wave-disturbed community in the Mediterranean Sea. Journal of Molluscan Studies 83: 325-332.
    Foord . 1890. Notes on the palaeontology of western Australia. Geol. Mag., (1890): 145155, pls 68.
    Fortič A, Trkov D, Lipej L, et al. 2021. New evidence of the occurrence of Knoutsodonta pictoni (Nudibranchia, Onchidorididae) in the Northern Adriatic. Anali za istrske in mediteranske študije - Annals for Istrian and Mediterranean Studies. 31(2):261–266.
    Furfaro G, Trainito E. 2017. A new species from the Mediterranean Sea and North-Eastern Atlantic Ocean: Knoutsodonta pictoni n. sp. (Gastropoda, Heterobranchia, Nudibranchia). Biodiversity Journal, 2017, 8 (2): 725–738.
    Hallas J, Gosliner TM. 2015. Family matters: The first molecular phylogeny of the Onchidorididae Gray, 1827 (Mollusca, Gastropoda, Nudibranchia). Molecular Phylogenetics and Evolution 88: 16-27.
    Sánchez-Tocino L. 2018. El Litoral de Granada - Opistobranquios. El Litoral de Granada. Available from
    Toll L, Ballesteros M. 2017. “Opistobranquios” (Mollusca: Gastropoda) de la colección malacológica Lluís Dantart. Spira 6 (2017): 171–184.
    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) "Knoutsodonta pictoni" in OPK-Opistobranquis. Published: 15/09/2015. Accessed: 04/03/2024. Available at (

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