Thordisa filix

Thordisa filix (Pruvot-Fol, 1951)

Thordisa filix by Manuel Ballesteros

Class: Gastropoda  Cuvier, 1797
Subclass: Heterobranchia  J.E. Gray, 1840
Clade: Euthyneura  Spengel, 1881
Clade: Nudipleura  Wägele & Willan, 2000
Order: Nudibranchia  Cuvier, 1817
Suborder: Euctenidiacea  Tardy, 1970
Infraorder: Doridacea  Thiele, 1931
Superfamily: Doridoidea  Rafinesque, 1815
Family: Discodorididae  Bergh, 1891
Genus: Thordisa  Bergh, 1877
Species: Thordisa filix  Pruvot-Fol, 1951

This species can reach 40 mm in length, but usually the cited specimens measure between 15 and 25 m in length. The color of the animal is a more or less homogeneous yellow with 1-2 dark areas in the mantle due to internal viscera, however, some specimens are coloured in lighter shades. The dorsum has numerous conical or slightly digitiform (finger like) tubercles and other filiform (thread like) tubercles sparser and coloured brown at the tip, forming a line of 5-6 tubercles in the center of the dorsum. The dorsum is very spiculous, as are the tubercles, which have spicules on their base in a starry arrangement. The rhinophores are yellow but have a thin brown pigmentation in the lamellae, the apex is whitish; the rhinophoric sheath is rather high and its upper edge is tuberculate. The gill consists of four tripinnate gill leaves that remain high and growing from a single basal protuberance; they are thin and semitransparent but with a light brown raquis. Branchial sheath is slightly raised and its upper edge is also tuberculate. In the center of the gill leaves lies the anal papilla, which is quite high, brownish and with 6-8 lobulations with rounded tips. The foot is relatively narrow, coloured uniform yellow and is furrowed and cleft on the front side. The mouth is located in a highly developed oral protuberance and has two whitish elongated labial palps. The genital orifice is very apparent and it is positioned on the underside of the mantle, to the right of the body.

This is a species living at a certain depth on the continental shelf, so it is difficult to observe by scuba diving. Very few details of its biology are known. Most of the known specimens have been collected by commercial trawling on soft or maerl bottoms at depths of 40-150 m. Schmekel cites that the spawn is an spiral ribbon with yellow eggs of about 120 microns. It’s supposed to feed on sponges, like other species of the same genus.


  • Thordisa. Woman name of Old Norse origin, cited in the Sagas. A fair woman to look on, high-minded, and rather hard of heart.
  • Filix. Latin word meaning fern, bracken, probably related to the shape of the gills.

T. filix has been cited so far in the western Mediterranean (Banyuls, Gulf of Naples, Spanish Levantine coast, Catalonia, Mallorca) and in Turkey, and there is also one citation of the species in the coasts of Portugal, which would be the only one out of the Mediterranean Sea. In the Catalan coast it is a relatively common species in commercial fishing grounds like La Planassa, off Blanes (Costa Brava), between 100 and 150 meters deep, a bottom rich in sponges, cnidarians, crustaceans, molluscs and fish.

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

References for the species: Thordisa filix

    Portugal: García-Gómez et al. (1991), Calado et al. (1999). Levante: Templado, Luque and Moreno (1988). Catalunya: Cervera et al. (1988), Domènech et al. (2006).

    General: Cattaneo-Vietti, Chemello, & Giannuzzi-Savelli, 1990:93[P]; Nordsieck, 1972:62; Pruvot-Fol, 1954b:252; Schmekel, 1970:198; Schmekel & Portmann, 1982:93[P]; Vicente, 1967:151

    Sources: Cervera et al., 2004, Ballesteros, 2007 & 2016, McDonald, 2006 and other sources.


    Western Mediterranean:
    Eastern Mediterranean:
    Atlantic Ocean:
This chart displays the observation probability for Thordisa filix based on our own records.

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Further reading

Cite this article as:

Ballesteros, Manuel, Enric Madrenas, Miquel Pontes et al. (2012-2017) "Thordisa filix" in OPK-Opistobranquis, Published: 29/08/2012, Accessed: 18/12/2017 at (

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