Marionia gemmii

Marionia gemmii Almón, Pérez & Caballer, 2018

Marionia gemmii @ Ria de Arousa, Galicia, Spain by Jacinto Pérez Dieste (GEMM)













































Marionia gemmii  Almón, Pérez & Caballer, 2018

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 1292043).
Big cream coloured body, up to 200 mm long, covered with warts of the same color, with purple and white variable sized dots scattered along the body surface. Warts are irregular in shapes and sizes, with a scale-like appearance. The white spots have a calcareous scab-like appearance. The notum and the sides of the body are covered by an orange colour pattern in the dorsum, black in the body walls, forming a reticula delimiting the edges of the warts. There is a characteristic thick orange band along the notum midline, irregularly covered by patches of warts, wider and in fewer numbers in the head, gradually narrowing in size but increasing in numbers towards the tail. The rhinophores are cream coloured and cylindrical in shape, branched at the tips and with a rhinophoral sheath with a narrower border than the base, quite wide in itself. The tripinnate filaments surrounding the tips of the rhinophores are retractile and coloured light brown. Rhinophoral sheaths are covered with light brown warts.The head ends in a bilobulated “velum” provided with 8 sac-like well spaced papilla on each lobe of the velum. Each papilla has 3 to 5 digitiform tubercles. There is one oral tentacle on each side of the mouth. There are 7 to 8 arborescent gills along each side of the notum, all of them similarly sized but the ones closer to the tail, that are smaller. Each gill branches in two several times, giving them a “bushy” look. The anus is located between the fourth and fifth pair of gills on the right side of the body, while genital opening is located below the third gill, also on the right side. The foot is large and muscular, sprayed with white spots, and both the front and back ends are rounded.

This species has been observed at depths between 18 and 40 meters. It apparently feeds exclusively on Leptogorgia sarmentosa red gorgonian, very common in the type locality. The spawn is quite large, formed by a white coil tightly attached to the gorgonian branches, where the eggs are clearly visible to the naked eye. This nudibranch begins swimming by strong body contractions when disturbed (see attached video).


  • Marionia. In honor to Prof. Antoine-Fortuné Marion, (1846-1900), French zoologist and professor / director of the Natural History Museum of Marseille, who during his school years in Aix was a friend of the artist to be Paul Cézanne, who later painted his portrait.
  • Gemmii, in honour of the non-profit association Grupo de Estudo do Medio Mariño (GEMM).

At the time of its description Almón et al. (2018) this species was known only from the coasts of Galicia (Spain) and the Atlantic coasts of Andalucia (Spain), but Trainito et al (2021) reported it in the Mediterranean coasts of France and Italy.
It has been historically overlooked or confused with other species, particularly Tritonia hombergii, all records should be reevaluated and clarified. Specifically, it seems clear that the T. hombergii record found by Rolán et al. (1991) in the Ría de Vigo could be M. gemmii given that the studied specimen shows a radular morphology (Rolán et al. 1991: fig. 1B–C) identical to that of M. gemmii. Likewise, the specimen from the Gulf of Cádiz studied by Almón et al (2018) also fits the description of M. gemmii, which suggests that the Andalusian record of T. hombergii by García-Gómez (1982) could actually belong to M. gemmii as well. Other Iberian records of T. hombergii (Hidalgo 1916; Ros 1975) lack any description, so the whole distribution range of this species has to be revised.
The discovery of a 20 cm long conspicuous new species of nudibranch in the coasts of Europe is absolutely unexpected, since this region has been intensively studied for the last 250 years, but this is not a strange case, as two other species of the same family have been described in the last eight years: Tritonia taliartensis Ortea & Moro, 2009 from the Canary islands (Ortea et al. 2009), and Tritonia coralliumrubri Doneddu, Sacco & Trainito, 2014, whose distribution is so far documented only from the island of Sardinia (Doneddu et al. 2014).

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

Similar species
M. gemmii can be confused with M. blainvillea but they can be distinguished by its size: 200mm vs. 60mm maximum recorded lengths. Also the colour pattern is different among these species, M. blainvillea is pale pink to translucent orange or dark brown, while M. gemmii is basically cream coloured with scattered purple and white spots; also M. blainvillea has the dorsal band coloured reddish to bright orange with 3–4 transversal whitish bands, not present in M. gemmii; M. blainvillea has a pinkish rhinophoral stalk while in M. gemmii it is cream-coloured; M. blainvillea has the tip of the rhinophores coloured orange to yellowish, M. gemmii has them cream-coloured; M. blainvillea has numerous and contiguous fingerlike small papillae, branching on the top, along the velum ridge, while M. gemmii has only 8 separated sac-like papillae present on each velum lobe.
Marionia gemmii could also be confused with T. hombergii (García-Gómez 1982; Rolán et al. 1991; Cervera et al. 2006), but both species can be easily distinguished by several external key characters. M. gemmii lacks tubercles in the mantle, present in T. hombergii; M. gemmii has fewer papillae along the velum edge, 8 sac-like papillae with 3-5 digitiform processes in the top versus 10–40 papillae with smooth digitiform tips in mature specimens of T. hombergii. Although the general colour pattern of T. hombergii is greatly variable, it never shows the reticulated scale-like pattern nor the central orange band on the notum, quite evident in M. gemmii. T.hombergii spawns consist on a wide creamish white cord, with several turns forming a globular mass generally coiled around a rock, while M. gemmii lays its eggstring among the gorgonian branches. Also T. hombergii typically feeds on the soft coral Alcyonium digitatum, and lays its eggs on the substrate where the coral grows, while M. gemmii lays its eggs on the red gorgonian Leptogorgia sarmentosa, which appears to be its main food source.


    Western Mediterranean: ★☆☆☆☆
    Eastern Mediterranean: ☆☆☆☆☆
    Atlantic Ocean: ★☆☆☆☆
[wpbi_chart type="bar" id="1" height="250" /]

This chart displays the monthly observation probability for Marionia gemmii based on our own records.



More pictures


    Almón B, Pérez Dieste J, Caballer M. 2018. Expect the unexpected, a new large species of Marionia (Heterobranchia, Nudibranchia, Tritoniidae) from western Europe. Invertebrate Systematics, 32: 892–908.
    García-Gómez JC. 1982. Contribución al conocimiento de los opistobranquios del litoral andaluz. Actas II Simposio Ibérico de Estudios del Bentos Marino III: 235-241.
    Hidalgo JC. 1916. Datos para la fauna española (Moluscos y Braquiópodos). Boletín de la Real Sociedad Española de Historia Natural 16: 235-246.
    Rolán E, Rolán-Álvarez E, Ortea J. 1991. Sobre la captura en Galicia (NO de España) de Tritonia hombergi Cuvier, 1803 y Babakina anadoni Ortea, 1979 comb. nov. (Mollusca: Nudibranchia). Iberus 10 (1): 113-117.
    Ros J. 1975. Opistobranquios (Gastropoda: euthyneura) del litoral ibérico. Investigacion Pesquera. 39(2):269–372. Available from
    Trainito E, Fantin M, Torsani F, et al. 2021. So large yet so unnoticed: the case of Marionia gemmii Almón, Pérez & Caballer, 2018 (Heterobranchia: Tritoniidae) in the Mediterranean Sea. Cahiers de Biologie Marine. 62:65–70.

    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:

Pontes, Miquel, Manuel Ballesteros, Enric Madrenas (2023) "Marionia gemmii" in OPK-Opistobranquis. Published: 07/01/2019. Accessed: 22/04/2024. Available at (

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