Okenia mediterranea

Okenia mediterranea (von Ihering, 1886)

Okenia mediterranea @ L'Escala, Spain by Enric Madrenas













































Okenia mediterranea  (Ihering, 1886)

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 140040).

  • Idalia mediterranea Ihering, 1886

This species measures up to 15 mm and has an oval shaped body coloured translucent white with many surfaces covered with opaque white, and with many yellow and reddish orange spots on the dorsum of most specimens. There are 9-12 pairs of lateral papillae tipped in orange over yellow pigment, the foremost pair longer than the rest, and the rearmost last two papillae joined at their bases on each side (Cervera et al. 1991). There is a ridge of 4-5 short, partly fused papillae along the dorsum midline, running from the rhinophores to the gills, also coloured in orange over yellow, and a row of 2-3 similarly coloured short papillae or tubercles (only present in adult specimens) on each side of the central ridge. A less common colour form shows yellow markings only (Rudman, 2001). Gills and rhinophores are relatively long and coloured with the same pattern as the other body processes. Rhinophores have 12-20 fine lamellae and the gill has 5-9 unipinnate white leaves with a yellow rachis, with 3-15 lamellae each (Cervera et al. 1991), surrounding a prominent anal papilla. The genital pore is located on the right flank of the animal, behind the rhinophores. The head has a bilobed frontal veil, with a yellow spot on each corner and the foot has a triangular shape at the tail, which is white with a yellow median line, edged with red spots in larger animals.

This species apparently feeds on the ctenostome encrusting bryozoan Alcyonidium mytili Dalyell, 1848 (see Cervera et al., 1991), despite Cattaneo-Vietti et al (1990) reported it feeding on the red gorgonian Paramuricea clavata and this information was used by other authors. The bathymetric range was reported in the coralligenous areas below 30 meters deep, but we have found this animal in much shallower water (12-15 meters), so this has to be revised. Its spawn consists on a circular shaped ribbon 10-12mm long, laid in a usually incomplete circle on the Alcyonidium bryozoan. Egg capsules measure between 71-97 microns and contain a single spherical white egg of  58-78 microns of diameter. Okenia mediterranea could be mistaken with other Okenia species, but colouration and papillae patterns differ. Okenia sapelona (Marcus & Marcus , 1967) is a very similar species (only differs on a blue tone of the white surfaces) that could correspond to a Western Atlantic distribution of Okenia mediterranea (see Valdés & Ortea, 1995 and Rudman, 2001), if this was the case O. mediterranea would become an amfiatlantic species. Confusion arises from the fact this species external features appear to change with age (Valdés & Ortea, 1995).


  • 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”.
  • Mediterranea. From Latin “médium”, middle, interspace, intermediate space, center + “terra”, Earth. From the Mediterranean Sea.

This species has been reported in Naples, Italy (Ihering, 1886; Schmekel, 1979; Schmekel & Portmann, 1982), in Numana, Italy (Cristian Magnani in Rudman, 2001), in Sicily, Italy (Valdés & Ortea, 1995), in Lecce, Italy (Fabio Vitale & Cataldo Licchelli, 2016), in Antalya, Turkey (Haluk Akbatur in Rudman, 2001), also in Granada, Spain (Sánchez-Tocino, 2000), in Algeciras, Spain (Alma Sánchez in Rudman, 2001), in Almeria, Spain (Moreno & Templado, 1998), in Vigo, Spain (Valdés & Ortea, 1995; Carlos Fernández-Cid, 2017), in Palamós, Spain (Enric Madrenas, 2009), in L’Escala, Spain (Enric Madrenas, 2017) and in Illes Medes, Spain (Guillem Mas, 2013). Also in Sines, Portugal (Calado et al. 2003) and in Madeira, Portugal (Valdés & Ortea, 1995). It is considered very rare.

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


    Western Mediterranean:1 out of 5 stars
    Eastern Mediterranean:1 out of 5 stars
    Atlantic Ocean:1 out of 5 stars

This chart displays the monthly observation probability for Okenia mediterranea based on our own records.

More pictures


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Further reading

Cite this article as:

Ballesteros, Manuel, Enric Madrenas, Miquel Pontes (2012-2020) "Okenia mediterranea" in OPK-Opistobranquis, Published: 15/05/2012, Accessed: 24/09/2020 at (https://opistobranquis.info/en/vsIjq)

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