Polycerella emertoni

Polycerella emertoni  A.E.Verrill, 1880

Polycerella emertoni @ Delta de l'Ebre by Manuel Ballesteros
















































Polycerella emertoni  A. E. Verrill, 1880

 Classification according to Bouchet et al. (2017)
Taxonomic source: World Register of Marine Species (AphiaID: 140839).

  • Polycerella comyna Marcus Er., 1957
  • Polycerella conyna Er. Marcus, 1957
  • Polycerella davenportii Balch, 1899
  • Polycerella recondita Schmekel, 1965

Body as high as wide, with a maximum observed length of 5-6 mm approximately, although most animals measure 3-4 mm in length. The body is translucent with bright yellowish tones and small dark brown or green spots scattered throughout the body. This coloration makes the animals very cryptic on the bryozoan they are living. The anterior part of the head is rounded, with no prolonged elongations but sometimes with small warts. Rhinophores are smooth (not laminated) and they are contractile. There are three small bipinnate gills located in the middle of the back, the one in the center is usually the largest. The anal papilla is located behind the middle gill. Some conical tubercles can be observed on the back, the most developed being the rearmost ones, in particular a symmetrical pair that are located behind the gills. The front of the foot has a pair of small triangular extensions. Moro et al. (2017) provide good pictures and drawings of the species.

This species lives in the Mediterranean and eastern Atlantic on soft bryozoans such as Amathia verticillata, until recently identified as Zoobotryon verticillatum (Waeschenbach et al., 2015), where it is perfectly cryptic because of its small size, shape and color. In the western Atlantic coasts it has been reported living on and feeding on the bryozoans Amathia gracilis (until recently known as Bowerbankia gracilis), Amathia distans and Bugula neritina (Clark, 1975; Valdés et al., 2006). The animals lays the spawn on the same bryozoan it feeds on; it is cylindrical and slightly curved, has a size of about 3 mm and contains about 100 eggs, each of which is enclosed by a capsule of about 100 microns (García-Gómez & Bobo, 1986) while eggs measure between 45 and 60 microns (Schmekel & Portmann, 1982). In the laboratory it has been observed that animals shrink down to a ball when they are disturbed (original data of the authors). Franz & Clark (1972) provide interesting information on the systematics, reproductive biology and zoogeography of the species.


  • Polycerella. Diminutive of Polycera.
  • Polycera, derives from Greek Polys, many and Keras, horn
  • Emertoni, in honor to James Henry Emerton (1847-1930), US arachnologist honoured to name several species of copepods, polychaete and gastropods.

Polycerella emertoni was originally described by the Atlantic coast of North America (Verrill, 1980). Since then it has been reported in different parts of the western Atlantic such as Cuba (Moro et al., 2017), Venezuela and Brazil (Tamsouri et al., 2014), as well as the eastern Atlantic coasts as Ghana (Edmunds, 1977 ), Canary Islands (Moro et al., 2017) and the Iberian Peninsula, where it is known from Portugal and the coast of Càdiz (Cervera et al., 2004). In the Mediterranean it was first seen observed in 1964 in Lake Fusaro (Italy) (Schmekel, 1965) and then reported in Malta, Greece and Tunisia coasts (Tamsouri et al., 2014). On the Catalan coasts, it was cited for the first time at the Coves of Cala Maset, in Sant Feliu de Guíxols (GROC, 2017). In the Delta de l’Ebre, an abundant population of P. emertoni has been found recently on the colonies of Amathia verticillata that grow at a very shallow depth on wooden or iron pylons or even on the shells of  the pen shell  Pinna nobilis. Numerous spawns have been observed on the colonies of A. verticillata in August 2018. It is possible that the wide distribution of the species is related to the almost cosmopolitan distribution (in warm and temperate seas) of the bryozoans that are their substrate and food. P. emertoni is considered as an invasive species in the Mediterranean (Zenetos et al., 2004) more than an amphyatlantic species.

Known georeferenced records of the species: Polycerella emertoni
: 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 Polycerella emertoni based on our own records.


Polycerella emertoni on Amathia verticillata, by Judith Camps © 2018


More pictures


    Abbott RT. 1974. American seashells. The marine mollusca of the Atlantic and Pacific coast of North America. Van Nostrand, New York. 663 pp., 24 pls. [October 1974].
    Balch FN. 1899. List of marine Mollusca of Coldspring Harbor, Long Island, with descriptions of one new genus and two new species of nudibranchs. Proc. Boston Soc. Nat. Hist. 29(7):133-162, pl 1.
    Ballesteros M, Madrenas E, Pontes M. 2023. OPK - Opistobranquis. Available from https://opistobranquis.info/.
    Ballesteros M, Pontes M, Madrenas E. 2019. Els nudibranquis del mar català. Figueres: Brau Edicions. 192 p.
    Ballesteros M, Pontes M, Álvarez G, et al. 2023. The hidden life of coastal cities. The case of marine biodiversity in Barcelona (Spain). Available from https://doi.org/10.13140/RG.2.2.16154.52165.
    Ballesteros M, Pontes M, Álvarez G, et al. 2023. La vida oculta de las ciudades costeras: El caso de la biodiversidad marina en Barcelona (España). VIMAR Vida Marina. Available from https://vidamarina.info/?p=5451.
    Bedulli D, Cattaneo-Vietti R, Chemello R, et al. 1995. Gastropoda Opisthobranchia, Divasibranchia, Gymnomorpha, Fascicolo 15, pp. 1-23.  In: A. Minelli, A. Ruffo, & S. La Posta (Eds.). Checklist delle specie fauna italiana. Bologna: Calderini (Checklist delle specie della Fauna Italiana).
    Behrens DW, Gosliner TM. 1988. The first record of Polycerella Verrill, 1881, from the Pacific, with the description of a new species. Veliger 30(3):319-324.
    Bergh LSR. 1883. Beitrage zu einer Monographie der Polyceraden. III. Verhandlungen der koniglich-kaiserlich Zoologisch-botanischen Gesellschaft in Wien (Abhandlungen) 33:135- 180, pls. 6-10.
    Bergh LSR. 1908. Malacologische Untersuchungen, In: Reisen im Archipel der Philippinen von Dr Carl Gottfried Semper. Zweiter Theil. Wissenschaftliche Resultate. Band 9, Theil 6, Heft 3; pp 119-181, pls. 9-12.
    Bergh R. 1892. System der Nudibranchiaten Gasteropoden. Malacologische Untersuchungen. In: Reisen im Archipel der Philippinen von Dr. Carl Gottfried Semper. Zweiter Theil#Wissenschaftliche Resultate. Band 7, Theil 5. [pp. 1–51, pls 1–4, Mar. 1897; pp. 53–115, pls 5–8, Dec. 1897; pp. 117–158, pls 9–12, Nov. 1898; pp. 159–208, pls 13–16, 27 Mar. 1900; pp. 209–256, pls 17–20, 29 Jan. 1901; pp. 257–312, pls. 21–24, 15 Oct. 1901; pp. 313–382, pls 25–29, 7 Oct. 1902].
    Caballer M, Ortea J, Rivero N, et al. 2015. The opisthobranch gastropods (Mollusca: Heterobranchia) from Venezuela: an annotated and illustrated inventory of species. Zootaxa 4034 (2): 201–256.
    Camps J, Prado P. 2018. Polycerella emertoni associated to Amathia verticillata in the Ebro Delta, NE Spain (Western Mediterranean). Mediterranean Marine Science 19: 673−689, p 675. https://doi.org/https://doi.org/10.12681/mms.19386.
    Camps J, Prado P. 2018. Polycerella emertoni associated to Amathia verticillata in the Ebro Delta, NE Spain (Western Mediterranean) [in] YOKEŞ et al (2018) New Mediterranean Biodiversity reports (november 2018). Medit. Mar. Sci., 19/3, 2018, 673-689.
    Camps J, Ballesteros M, Trobajo R, et al. 2020. Not all nudibranchs are carnivorous: trophic ecology of Polycerella emertoni in the Ebro Delta. Marine Ecology Progress Series 645: 67-82. https://doi.org/https://doi.org/10.3354/meps13379.
    Camps J, Ballesteros M, Trobajo R, et al. 2021. Are all nudibranchs carnivorous? Feeding behaviour of the cryptic nudibranch Polycerella emertoni associated with the pseudo-indigenous bryozoan Amathia verticillata. Available from http://www.umag.cl/facultades/ciencias/biologiamarina/wp-content/uploads/resumenes-xl-congreso-ciencias-del-mar-magallanes-biomarina-umag2021.pdf.
    Cattaneo-Vietti R, Barletta G. 1984. Elenco preliminare dei molluschi opistobranchi viventi nel Mediterraneo (Sacoglossa, Pleurobranchomorpha, Acochlidiacea, Aplysiomorpha, Nudibranchia). Bollettino Malacologico (Pubblicazione Mensile Edita dalla Societa Italiana di Malacologia) 20(9-12):195-218.
    Cattaneo-Vietti R, Chemello R. 1991. The opisthobranch fauna of a Mediterranean lagoon (Stagnone di Marsala, western Sicily). Malacologia 32(2):291-299.
    Cattaneo-Vietti R, Thompson TE. 1989. Mediterranean opisthobranch molluscs: a zoogeographic approach. Bollettino Malacologico (Pubblicazione Mensile Edita dalla Societa Italiana di Malacologia) 25(5-8):183-204.
    Cattaneo-Vietti R, Chemello R, Giannuzzi-Savelli R. 1990. Atlas of Mediterranean Nudibranchs. Rome, Italy: La Conchiglia. 264 p.
    Cervera JL. 1988. Notaspideos, ascoglosos y nudibranquios, (mollusca : opisthobranchia) de Andalucía Occidental con algunas referencias al litoral del Estrecho de Gibraltar : estudio faunístico y sistemático. Tesis Doctoral. Universidad de Sevilla. 312 h., 10 h. de lám. 84 il. n., 6 map. 30 cm p.
    Cervera JL, Templado J, García-Gómez JC, et al. 1988. Catálogo actualizado y comentado de los Opistobranquios (Mollusca, Gastropoda) de la Península Ibérica, Baleares y Canarias, con algunas referencias a Ceuta y la isla de Alborán. Iberus, supl. 1: 1-84.
    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.
    Clark KB. 1975. Nudibranch life cycles in the northwest Atlantic and their relationship to the ecology of fouling communities. Helgolander wissenschaftliche Meeresuntersuchungen 27: 28-69.
    Crocetta F. 2011. Marine alien mollusca in Italy, a review. Journal of the Marine Biological Association of the United Kingdom, 2012, 92(6), 1357–1365. https://doi.org/10.1017/S002531541100186X.
    Edmunds M. 1977. Larval development, oceanic currents, and origins of the Opisthobranch fauna of Ghana. Journal of Molluscan studies 43:301-308.
    Edmunds M. 1991. Does warning coloration occur in nudibranchs. Malacologia 32(2):241-255.
    Franz DR. 1968. Occurrence and distribution of New Jersey opisthobranchia. Nautilus 82(1):7-12.
    Franz DR, Clark KB. 1972. A discussion of the systematics, reproductive biology, and zoogeography of Polycerella emertoni and related species (Gastropoda: Nudibranchia). Veliger 14(3):265-270.
    Garcia FJ, Bertsch H. 2009. Diversity and distribution of the Gastropoda Opisthobranchia from the Atlantic Ocean: A global biogeographic approach. Scientia Marina. 73(1):153–160. https://doi.org/10.3989/scimar.2009.73n1153.
    García-Gómez JC. 2002. Paradigmas de una fauna insólita; Los moluscos opistobranquios del estrecho de Gibraltar (Serie Ciencias) 20: 397 pp. Instituto de Estudios Gibraltareños. Algeciras, Cádiz, Spain.
    García-Gómez JC, Bobo A. 1986. Un nuevo doridáceo para el litoral ibérico: Polycerella emertoni Verrill (1880) 1881 (Gastropoda: Nudibranchia). Bollettino Malacologico 22 (1-4): 49-56.
    García-Gómez JC, Cervera JL, García FJ, et al. 1991. Resultados de la campaña internacional de biología marina “Algarve 88”: moluscos opistobranquios. Bollettino Malacologico 27 (5-9): 125-138.
    Long SJ. 2006. Bibliography of Opisthobranchia 1554-2000. Bayside Books & Press, Tustin, CA, U.S.A. 672p.
    Marcus E d. BR. 1977. An annotated checklist of the western Atlantic warm water opisthobranchs. J. Molluscan Stud., Suppl 4:1-23.
    Marcus Er. 1957. On opisthobranchia from Brazil 2. Journal of the Linnean Society of London (Zoology) 43(292): 390-486.
    Marcus Er., Marcus Ev. 1960. Opisthobranchs from American Atlantic warm waters. Bull. Mar. Sci. 10(2):129-203.
    McDonald G. 2009. Bibliographia Nudibranchia. 2nd Online Edition, Annotated. 1072 pp  Institute of Marine Sciences, University of California, Santa Cruz. Available from http://escholarship.org/uc/item/8115h0wz.
    Megina C, Cervera JL. 2003. Diet, prey selection and cannibalism in the hunter opistobranch Roboastra europaea. Journal of the Marine Biological Association of the United Kingdom 83 (3): 489-495.
    Moro L, Ocaña O, Ortea J. 2017. Sobre la distribución de Polycerella emertoni Verrill,1880, (Mollusca: Nudibranchia: Polyceridae) en las costas atlánticas de África Continental, con observaciones sobre el género Amathia Lamouroux, 1812 (Bryozoo: Vesicularioidea), su alimento, en las islas Canarias. Vieraea 45: 83-88.
    Moro L, Ocaña O, Bacallado JJ, et al. 2017. Nota sobre tres babosas marinas (Nudibranchia y Sacoglossa) colectadas en las costas atlánticas de África (Cabo Espartel, Agadir y Dakhla), con un listado de especies acompañantes. Vieraea 45: 205-214.
    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.
    Pola M, Cervera JL, Gosliner JL. 2007. Phylogenetic relationships of Nembrothinae  (Mollusca: Doridacea: Polyceridae) inferred from morphology and mitochondrial DNA. Molecular  Phylogenetics & Evolution 43(3):726-742.
    Pola M, Cervera JL, Gosliner TM. 2006. Taxonomic revision and phylogenetic analysis of the genus Tambja Burn, 1962 (Mollusca, Nudibranchia, Polyceridae). Zoologica Scripta 35(5):491-530. Available from http://www.blackwell-synergy.com/doi/abs/10.1111/j.1463-6409.2006.00241.x.
    Pola M, Cervera JL, Gosliner TM. 2005. Review of the systematics of the genus Roboastra Bergh, 1877 (Nudibranchia, Polyceridae, Nembrothinae) with the description of a new species from the Galápagos Islands. Zoological Journal of the Linnean Society, 144(2): 167-189.
    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.
    Rios EC. 1975. Brazilian marine mollusks iconography, 331 pp, 91 pls. Fundacao Universidade do Rio Grande, Centro de Ciencias do Mar, Museu Oceanografico.
    Ros J. 1981. Desarrollo y estrategias bionómicas en los Opistobranquios. Oecologia aquatica 5: 147-183. Available from https://raco.cat/index.php/oecologiaaquatica/article/view/382034.
    Rudman W.B. et al. 1998 2010. Polycerella emertoni accessed through: Sea Slug Forum on 2014-12-14. Available from http://seaslugforum.net/showall/polyemer.
    Rufray X, Girard P, Le Bris S, et al. 2021. Liste commentée des limaces de mer de la lagune de Thau, Hérault. Les cahiers de la fondation Biotope. 36:1–189. Available from https://www.biotope.fr/download/230907/.

    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:

Camps, Judith; Manuel Ballesteros; Enric Madrenas; Miquel Pontes (2023) "Polycerella emertoni" in OPK-Opistobranquis. Published: 11/09/2014. Accessed: 05/03/2024. Available at (https://opistobranquis.info/en/?p=14197)

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