Cliopsis krohnii

Cliopsis krohnii Troschel, 1854

Cliopsis krohnii @ Lake Worth Lagoon, Florida, USA 2-10-2011 by Anne DuPont







































Cliopsis krohnii  Troschel, 1854

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 139185).
Taxonomic note: Marine Species Identification Portal recognizes three morphs:


  • Clio mediterranea Gegenbaur, 1855
  • Clionopsis krohnii (Troschel, 1854)
  • Clionopsis microcephalus Tesch, 1903
  • Clionopsis modesta Pelseneer, 1887
  • Cliopsis grandis Boas, 1886
  • Cliopsis modesta Pelseneer, 1887
  • Pneumodermon peronii auct. non Lamarck, 1819
  • Pneumodermon diaphanum Guerin, 1844
  • Trichocyclus mediterranea (Gegenbaur, 1855)

Cliopsis krohnii has a relatively large (up to 40mm), globular (more elongate in juveniles), soft, gelatinous body, with a clearly visible visceral core. The body is translucent in mature specimens, while in younger specimens may be tinted in yellow, light brown, light blue or gray. There is a rose tinge in the head area. It has two rounded fins placed very far forward, near the head. The head is small with highly developed nuchal tentacles without suctors. The terminal gill is located in the posterior side of the body and has four radiating crests connecting to an hexagonal crest surrounding the mucronate body apex. The foot is small and consists of three small median lobes visible between the wings. The mouth has an elaborate foregut, with a proboscis that can extend to two times its body length, chitinous hooks (with the hook sacs containing about 60 hooks) and cutting radular teeth. It lacks a shell but on its early embryonic stage.

As all gymnosomates, Cliopsis krohnii is a highly specialised carnivore predator which feeds on the phytoplankton feeding thecosomate pteropods of the genus Corolla sp. These Corolla catch their food with the aid of an enormous mucuous net (up to 2 meters in diameter) they cast out in front of them. When Cliopsis krohnii senses one of these feeding nets, it stops swimming and begins dragging the net in until Corolla is close enough for Cliopsis‘s long proboscis to reach out and cut the columellar muscle, which attaches Corolla to its shell (Rudman in Sea Slug Forum, 2010), then grasping its victim with the chitinous hooks. Cliopsis can eat animals three times its own size. It spends its whole life amidst plankton. The fins are used for swimming and they can propel the animal quite quickly. Like other gymnosomates it does not regulate buoyancy with ionic balance nor specialised buoyancy structures (Wrobel & Mills, 1998). 


  • Cliopsis. From Greek “Kleio”, Ocean’s daughter and sister of Beroe + “-opsis”, “similar to” or “shaped like”.
  • Krohnii. In honor of Dr. August David Krohn, (1803-1891), Russian zoologyst of German origin, he was a pionneer of marine biology and exchanged correspondence with Charles Darwin. He wrote about tunicates and also wrote essential chaetognath works in 1844 & 1853.

Cliopsis krohnii is found in all temperate and tropical seas where it is pelagic and lives amidst plankton at depths down to 1,500 m. (Wrobel & Mills, 1998). It has been found in the Pacific, in the temperate waters north of Southern California (Wrobel & Mills, 1998), also in Caribbean (OBIS, 2016), and in saltwater lagoons in Florida, USA (DuPont A., 2/10/2011, pers. comm.). In the Mediterranean is relatively abundant in the Tyrrhenian Sea and in the Ionian Sea, where it can be found near the coasts of Italy and Tunisia. Scarce in other Mediterranean locations (Riedl, R., 1986).

Known georeferenced records of the species: Cliopsis krohnii
: 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 Cliopsis krohnii based on our own records.

More pictures


    Ballesteros, M., E. Madrenas, and M. Pontes. 2023. OPK - Opistobranquis. (
    Barnich, R., and D. Uthe. 1998. The Gymnosomata (Gastropoda : Opisthobranchia) in the plankton of the French Mediterranean coast. Vie Et Milieu-Life and Environment. 48: 15–24.
    Boas, J. E. V. 1886. Spolia Atlantica. Bidrag til Pteropodernes. Morfologi og systematik samt til kundskaben om deres geografiske udbredelse. Kongelige Danske Videnskabernes-Selskabs Skrifter. Naturvidenskabelig og Mathematisk Afdeling (6)4(1): 1-231 pl. 1-6.
    Gegenbaur, C. 1855. Untersuchungen uber Pteropoden un Heteropoden. Ein Beitrag zur anatomie und Entiwicklungsgeschichte dieser Thiere. Wilhelm Engelmann, Leipzig pp. 228 pl. 1-8:
    Guerin Meneville, M. F. E. 1844. Iconographie du règne animal de G. Cuvier (Mollusques). Paris, London (Baillière): 1-64, atlas 38 pls.
    Pelseneer, P. 1887. Report on the Pteropoda, 1. The Gymnosomata. Report of the H M.S. Challenger, 19(4): .
    Riedl, R. 1983. Fauna und Flora der Mittelmeeres, ein systematischer Meeresfuhrer fur Biologen und Naturfreunde, 836 pp. Paul Parey, Hamburg & Berlin.
    Rolán, E. 2005. Malacological Fauna From The Cape Verde Archipelago. Part 1, Polyplacophora and Gastropoda. ConchBooks, Frankfurt, Germany.
    Rudman W.B. et al. 1998. Cliopsis krohni accessed through: Sea Slug Forum on 2014-12-14. (
    Tesch, J. J. 1903. Vorläufige Mitteilung über die Thecosomata und Gymnosomata der Siboga-Expedition. Tijdschrift der Nederlandsche Dierkundige Vereeniging (2) 9 (2): 111-117.
    Tesch, J. J. 1904. The Thecosomata and Gymnosomata of the Siboga Expedition. Siboga- Expeditie, Leiden, E.J. Brill, 52: 1-92.
    Troschel, F. H. 1854. Beitrage zur Kenntniss der Pteropoden. Archiv für Naturgeschichte, Berlin, 20 (1): 196-241, pl. 8-10.
    van der Spoel, S. 1976. Pseudothecosomata, Gymnosomata and Heteropoda (Gastropoda). Utrecht (Bohn, Scheltema & Holkema): 484 pp, 246 figs.
    Verrill, A. E. 1885. Results of the explorations made by the steamer “Albatross”, off the  northern coast of the United States, in 1883. United States Commission of Fish & Fisheries. Report of  the Commissioner for 1883, pt. 11, appendix D, Natural History & Biological Research, pp. 503-699,  pls. 1-44.
    Willan, R. C. 2009. Opisthobranchia (Mollusca) in Gordon, D.P. (ed.) New Zealand inventory of biodiversity. Volume one. Kingdom Animalia. Canterbury University Press, Christchurch.
    WoRMS Editorial Board. 2023. World Register of Marine Species. WoRMS. (

    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:

Pontes, Miquel, Manuel Ballesteros, Enric Madrenas (2023) "Cliopsis krohnii" in OPK-Opistobranquis. Published: 26/11/2016. Accessed: 28/02/2024. Available at (

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