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: ★★★★☆
    Eastern Mediterranean: ★★★★☆
    Atlantic Ocean: ★☆☆☆☆

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



More pictures


    Altimira C, Huelin MF, Ros J. 1981. Mol·luscs bentònics de les illes Medes (Girona). I. Sistemàtica. Butll. Inst. Cat. Hist. Nat. (Sec. Zool.), 47: 69-75.
    Ballesteros M. 2007. Lista actualizada de los opistobranquios (Mollusca: Gastropoda: Opisthobranchia) de las costas catalanas. Spira. 2(3):163–188.
    Ballesteros M. 1980. Contribución al conocimientos de los Sacoglosos y Nudibranquios (Mollusca: Opisthobranchia). Estudio anatómico, sistemático y faunístico de las especies del mediterráneo español. Tesis Doctoral. Barcelona: Universitat de Barcelona.
    Ballesteros M, Álvarez C, Mateo B. 1986. Aproximación a la fauna de opistobranquios de la isla de Menorca. Publicaciones del Departamento de Zoología (Barcelona) 12: 93-106.
    Ballesteros M, Pontes M, Madrenas E. 2015. Opisthobranch from Medes Islands (Marine Protected Area, Costa Brava, Catalonia, NE Spain): 40 years of study. Available from
    Ballesteros M, Madrenas E, Pontes M. 2016. Actualización del catálogo de los moluscos opistobranquios (Gastropoda: Heterobranchia) de las costas catalanas. Spira. 6:1–28.
    Ballesteros M, Madrenas E, Pontes M. 2024. OPK - Opistobranquis. Available from
    Betti F, Bavestrello G, Cattaneo-Vietti R. 2021. Preliminary evidence of fluorescence in Mediterranean heterobranchs. Journal of Molluscan Studies. 87:eyaa040.
    Bielecki S, Cavignaux G, Crouzet JM, et al. 2011. Des limaces de rêve.
    Canessa M, Bavestrello G, Cattaneo-Vietti R, et al. 2021. Rocky substrate affects benthic heterobranch assemblages and prey/predator relationships. Estuarine, Coastal and Shelf Science 38: 539-558. 261:1–13.
    Capdevila M, Folch J. 2009. Fauna malacològica del Parc Subaquàtic de Tarragona (el Tarragonès, Catalunya, Espanya). SPIRA Vol. 3 Núms. 1-2 Pàg. 33-51.
    Carmona L, Malaquias MAE, Gosliner TM, et al. 2011. Amphi-atlantic distributions and cryptic species in sacoglossan sea slugs. Journal of Molluscan Studies 77: 401–412.
    Cervera JL, García-Gómez JC. 1986. Moluscos opistobranquios del litoral occidental andaluz: nuevas aportaciones faunísticas. Iberus 6 (2): 201-207.
    Cervera JL, Calado G, Gavaia C, et al. 2004. An annotated and updated checklist of the opisthobranchs (Mollusca: Gastropoda) from Spain and Portugal (including islands and archipelagos). Boletín Instituto Español de Oceanografía, 20 (1-4): 1-111. L.
    Dacosta JM, Pontes M, Ollé i Callau A, et al. 2009. Seguiment de mol·luscs opistobranquis a la platja des Caials (Cadaqués, Alt Empordà). Contribució al catàleg del Parc Natural de Cap de Creus. Annals de l’Institut d’Estudis Empordanesos. 40:107–130.
    De Fez S. 1974. Ascoglosos y Nudibranquios de España y Portugal. Valencia, Spain: Consejo Superior de Investigaciones Científicas. 325 p.
    Furfaro G, Modica MV, Oliverio M, et al. 2014. Phenotypic diversity of Thuridilla hopei (Vérany, 1853) (Gastropoda, Heterobranchia, Sacoglossa). A DNA-barcoding approach. Biodiversity Journal, 5 (2): 117–130.
    Furfaro G, Vitale F, Licchelli C, et al. 2020. Two Seas for One Great Diversity: Checklist of the Marine Heterobranchia (Mollusca; Gastropoda) from the Salento Peninsula (South-East Italy). Diversity. 12(12):171.
    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.
    Gascoigne T. 1985. A provisional classification of families of the order Ascoglossa (Gastropoda: Nudibranchiata). Journal of Molluscan Studies, 51: 8-22.
    Göthel H. 1994. Fauna marina del Mediterráneo. Barcelona: Ediciones Omega. 320 p.
    Huelin MF, Ros J. 1984. Els mol·lucs marins de les illes Medes In: Els sistemes naturals de les Illes Medes. Arxius de la Secció de Ciéncies, J Ros et al (eds) 73: 457-500. IEC. Barcelona, Spain.
    Jensen KR. 1992. Anatomy of some Indo-Pacific Elysiidae (Opisthobranchia: Sacoglossa (= Ascoglossa)), with a discussion of the generic division and Phylogeny. Journal of Molluscan Studies. 58:257–296.
    Laetz EMJ, Rühr PT, Bartolomaeus T, et al. 2016. Examining the retention of functional kleptoplasts and digestive activity in sacoglossan sea slugs. Organisms Diversity & Evolution (2016) pp 1-13.
    Long SJ. 2006. Bibliography of Opisthobranchia 1554-2000. Bayside Books & Press, Tustin, CA, U.S.A. 672p.
    Luque AA. 1983. Contribución al conocimiento de los gasterópodos marinos de las costas de Málaga y Granada. Iberus 3: 51-74.
    Malaquias M, Calado G, Padula V, et al. 2009. Molluscan diversity in the North Atlantic Ocean: new records of opisthobranch gastropods from the Archipelago of the Azores. Marine Biodiversity. 2:e38.
    Marín A, Ros JD. 1989. The Chloroplast-Animal Association in Four Iberian Sacoglossan Opisthobranchs Elysia timida, Elysia translucens, Thuridilla hopei and Bosellia mimetica. 22nd European Marine Biology Symposium, Barcelona, Spain, August 17-22, 1987. Scient. Mar. 53(2-3):429-440.
    Martín-Hervás MR, Carmona L, Malaquias MAE, et al. 2021. A molecular phylogeny of Thuridilla Bergh, 1872 sea slugs (Gastropoda, Sacoglossa) reveals a case of flamboyant and cryptic radiation in the marine realm. Cladistics.(2021):1–30.
    Martínez-Chacón M. 2018. Nudibranquios de la isla de Tarifa, pequeñas joyas del estrecho de Gibraltar. Junta de Andalucía. Consejería de Medio Ambiente y Ordenación del Territorio. Available from
    McDonald G. 2009. Bibliographia Nudibranchia. 2nd Online Edition, Annotated. 1072 pp  Institute of Marine Sciences, University of California, Santa Cruz. Available from
    Ozturk B, Dogan A, Bitlis-Bakir B, et al. 2014. Marine Molluscs of the Turkish Coasts: An Updated Checklist. Tübitak, Turkish Journal of Zoology 38.
    Parera A, Pontes M, Salvador X, et al. 2020. Sea slugs (Mollusca, Gastropoda, Heterobranchia): the other inhabitants of the city of Barcelona (Spain). Butlletí de la Institució Catalana d’Història Natural, 84: 75-100.
    Pereira F. 1981. Gasterópodos del litoral mediterranáo español. III. Isla de Faradell, Gerona. Investigación Pesquera 45 (1): 175-179.
    Pereira F, Ballesteros M. 1982. Gasterópodos del litoral mediterranáo español. II. Tossa de Mar, Gerona. Actas I Simposio Ibérico Bentos Marino, 1: 223-235.
    Perrone AS. 1991. Un caso di teratologia parapodiale in Thuridilla hopei (Verany, 1853) dal Golfo di Taranto (Opisthobranchia Sacoglossa). A Case Of Parapodial Teratology In Thuridilla hopei Verany 1853 From The Gulf Of Taranto Opisthobranchia Sacoglossa. Boll Malacol 27 (5-9). 1991. 121-124.
    Pontes M, Dacosta JM, Ollé i Callau A, et al. 2023. M@re Nostrum. Available from
    Pontes M, Salvador X, Parera A, et al. 2021. Biodiversity in anthropized marinas. The case of the Barcelona Forum bathing area (Spain). Barcelona: Institució Catalana d’Història Natural (Monografies de la Societat Catalana d’Història Natural). 68 p.
    Prkić J, Petani A, Iglić Ð, et al. 2018. Stražnjoškržnjaci Jadranskoga Mora: Slikovni Atlas i Popis Hrvatskih Vrsta / Opisthobranchs of the Adriatic Sea: Photographic Atlas and List of Croatian Species. Bibinje: Ronilaćki Klub Sveti Roko. 464 p. Available from
    Riedl R. 1983. Fauna und Flora der Mittelmeeres, ein systematischer Meeresfuhrer fur Biologen und Naturfreunde, 836 pp. Paul Parey, Hamburg & Berlin.
    Ros J. 1975. Opistobranquios (Gastropoda: euthyneura) del litoral ibérico. Investigacion Pesquera. 39(2):269–372. Available from
    Ros J. 1978. Distribució en l’espai i en el temps dels opistobranquis iberics, amb especial referencia als del litoral catalá. Butll. Inst. Cat. Hist. Nat., 42 (Sec. Zool., 2): 23-32.
    Ros J. 1985. Distibución batimétrica, abundancia y diversidad de las poblaciones de moluscos bentónicos del litoral catalán. Miscelánea Zoologica 9: 109-126.
    Ros J. 1973. Opistobranquios (Gastropoda: Euthyneura) del litoral ibérico : Estudio faunístico y ecológico [Tesis Doctoral]. Barcelona: Universitat de Barcelona. 285 p.
    Ros J, Altimira C. 1977. Comunidades bentónicas de sustrato duro del litoral NE español; V Sistemática de moluscos. Miscelánea Zoológica 4 (1): 43-55.
    Rudman W.B. et al. 1998 2010. Thuridilla hopei accessed through: Sea Slug Forum on 2014-12-14. Available from
    Sánchez Tocino L. 2001. Thuridilla hopei accessed through: Opistobranquios de la Costa de Granada on 2014-12-14. Available from
    Sánchez-Tocino L. 2018. El Litoral de Granada - Opistobranquios. El Litoral de Granada. Available from
    Schmitt V, Waegele H. 2011. Behavioral adaptations in relation to long-term retention of endosymbiotic chloroplasts in the sea slug Elysia timida (Opisthobranchia, Sacoglossa). Thalassas. 27(2):225–238. Available from ://WOS:000291629300013.
    Templado J, Villanueva R. 2010. Checklist of Phylum Mollusca. pp. 148-198 In Coll, M., et al., 2010. The biodiversity of the Mediterranean Sea: estimates, patterns, and threats. PLoS ONE 5(8):36pp.

    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) "Thuridilla hopei" in OPK-Opistobranquis. Published: 14/05/2012. Accessed: 18/05/2024. Available at (

To copy this cite click on the right button.