Thuridilla hopei

Thuridilla hopei (Verany, 1853)

Thuridilla hopei by Enric Madrenas




































Thuridilla hopei  (Vérany, 1853)

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 139687).

  • Actaeon hopei Vérany, 1853
  • Elysia cyanea Mamo in Caruana, 1867
  • Elysia splendida Grube, 1861

The visually striking individuals of this species measure between 15 and 20 mm in length, despite the are findings of animals up to 30 mm (excluding rhinophores). The body is narrow and elongated and its base color is usually dark purple, almost black, the foot of a somewhat lighter shade. Some animals may have dark brown bodies instead of purple. External side of parapods shows a bright orange band on the edge close to sky blue and yellow bands. The inside of the parapods it is dark purple or dark brown. Along the body there could be white or pale yellow spots that may form a discontinuous longitudinal line. Rhinophores are long and auriculated and share the color of the body, but having an iridescent yellowish white longitudinal stripe on its inner surface, at times they are bordered of sky blue color. The mouth has a striking orange lower labia. This coloration extends somewhat by the side of the head region, also dotted with sky blue dots. The foot is narrow, with rounded edges. According to the paper by Furfaro et al., (2014), it seems that the color patterns of Thuridilla hopei are related to the depth where it lives. Deep water specimens seem to be bluish and smooth, with no spots, while shallow water specimens have a pattern of dots and dashes.

Thuridilla hopei individuals are pretty active and can be found on rocks with algal coating, both on photophilic and sciaphilic algae communities full of hidrarians, sponges and briozoans. Some animals could be found under stones. Parapods are usually in touch with the body while the animal moves around, but can be opened laterally when it is at rest. Herbivorous as most sacoglossans, this species is able to retain, inside of its body, functional chloroplasts from the algae that it feeds on, to obtain extra nutrients by photosynthesis. Mating, described by Gascoigne (1985), is reciprocal: two animals join their heads by the right side, then extend their penises and inject sperm into the other’s sperm sac (named “bursa copulatrix”) which has an external opening right behind the pericardial zone behind of the head. However there is no internal connection from the sperm sac to the rest of the reproductive system, so how sperm gets to fertilise the eggs is still unknown. Spawn is laid in the form of a flat spiral on the substrate. Development in Thuridilla hopei has been described by Thompson & Salghetti-Drioli (1984) as lecithotrophic (a mode of embryonic development in which the yolk of an egg provides all the nourishment). Both eggs and extra-capsular yolk are red at first, the colour of the eggs fading as embryological development progresses (Jensen, 1992). Thuridilla hopei has the capability to obtain defensive substances such as thuridillines, extracted from diterpenoid molecules obtained from its algal diet.


  • Thuridilla. Derived from Thurida (the daughter of Thord of Höfdi), a character of the Icelandic Saga of Viga-Glum.
  • Hopei. In honor of Rev. Frederick William Hope, (1797-1862). Rev. Hope was a famous and wealthy amateur entomologist who established the Hope Professorship at Oxford, given for the first time to Hope’s follower Westwood. Hope’s only foray into the marine area was in his “Catalogo dei Crostacei Italiani” published in Naples in 1851, a catalog of crustaceans from the Mediterranean, 48 pages and a plate.

It is a widespread species throughout the Mediterranean, from Spain to Turkey or Israel. Out of this area it has only been cited in the Atlantic coasts of Huelva (Spain, NE Atlantic) and the Macaronesia (Canary Islands, Azores and Madeira), where specimens of Thuridilla hopei, traditionally ascribed to the Caribbean Thuridilla picta (Verril, 1901) due to a similar colour pattern (see Cervera et al., 2004; Malaquias et al., 2009) finally belong to Thuridilla hopei after the molecular studies conducted by Carmona et al. (2011). In the Iberian Peninsula is common throughout the Mediterranean coast from the Catalan coast down to the Strait of Gibraltar. In Catalonia it has been cited or observed along the coastline of both the Costa Brava, Maresme and many localities south of Barcelona.

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


    Western Mediterranean:4 out of 5 stars
    Eastern Mediterranean:4 out of 5 stars
    Atlantic Ocean:1 out of 5 stars

This chart displays the monthly observation probability for Thuridilla hopei based on our own records.


Thuridilla hopei by Pascal Girard


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Further reading

Cite this article as:

Ballesteros, Manuel, Enric Madrenas, Miquel Pontes (2021) "Thuridilla hopei" in OPK-Opistobranquis. Published: 14/05/2012. Accessed: 03/08/2021. Available at (

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