Okenia impexa

Okenia impexa (Marcus Er., 1957)

Okenia impexa @ Canarias by Ortea et al., (2009)
















































Cargoa impexa   (Er. Marcus, 1957)

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 1723343).
This is a species whose specimens rarely exceed 4-5 mm in length. The body is high and relatively wide. The general body color is hyaline white, sometimes with yellowish or cream tones, while internal organs can be seen by transparency inside of the body. There are numerous dark brown scores scattered throughout the body that may form, in some specimens, a big dark stain in the center of the back. The head has a slightly lobed frontal veil with 4 thin and long tentacular processes. The rhinophores are thick and have up to 8 lamellae that cover the rear and lateral areas of the rhinophore but not the front area. The edge of the dorsum has 6 papillae on each side, elongated and enlarged in a bulbous shape near the apex. The last two papillae on each side grow from a common base. There is also an odd papilla in the center of the back, just in front of the gill. The papillae are coloured in a lighter shade than the body. Gill consists of three unipinnate leaves surrounding the anal papilla. The foot is wide and pointed on the rear side and the mouth and has two rounded bumps on each side.

This rare species has been cited on algae of the genus Halimeda and other coralline algae (Schmekel, 1979), on masses of floating algae in the Atlantic and on the bryozoan Margaretta cereoides, that could be its prey (Ortea et al. 2009). The spawn consists on a bean-shaped mass of 3 mm in length, containing about 500 white eggs (Eyster, 1980).


  • Okenia. In honor of Prof. Dr. Ludwig Gilbert Lorenz Oken, (1779-1851), German natural philosopher, editor of the magazine “Isis” and publisher of the book “Lehrbuch der Naturgeschichte”.
  • Impexa. From Latin “impexus”, uncombed.

Okenia impexa is an amfiatlantic species because since its description by Ernst Marcus in 1957 for Brazilian waters, it has been observed in North Carolina, in Cuba, Puerto Rico and Cape Verde (Valdes & Ortea, 1995), also in the Canary Islands (Ortea et al. 2009). Records from the Mediterranean Sea (Schmekel, 1979 and others) refer to the recently described Okenia problematica (Pola et al., 2019).

Known georeferenced records of the species: Okenia impexa
: 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 Okenia impexa based on our own records.

More pictures

    We have no (more) pictures for Okenia impexa


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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

Cite this article as:

Ballesteros, M., Madrenas, E. & Pontes, M. (2023) "Okenia impexa" in OPK-Opistobranquis. Published: 24/05/2012. Accessed: 17/04/2024. Available at (https://opistobranquis.info/en/?p=1152)

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