The exotic freshwater mollusc Helisoma duryi is a popular ornamental freshwater snail used to control microalgae in aquariums which occurs now as an introduced species in aquatic habitats of Europe, Africa and South America. We report the first finding of an acclimated population of H. duryi in Morocco and discuss the possible role of the trade of aquatic species in its introduction. While currently located in a single locality out of > 100 localities sampled, further studies are required to monitor its presence and expansion and to improve our knowledge about their possible impact on native freshwater communities.

Keywords: Alien invasive species; Aquarium trade; Freshwater habitats; North Africa; Planorbidae.


Primera cita del caracol exótico Helisoma duryi (Wetherby, 1879), (Gastropoda: Planorbidae) en Marruecos

El molusco exótico Helisoma duryi es un popular caracol ornamental de agua dulce que se utiliza para controlar las microalgas en los acuarios. Ahora se presenta como una especie introducida en hábitats acuáticos de Europa, África y América del Sur. Presentamos el primer hallazgo de una población aclimatada de H. duryi en Marruecos y el norte de África. A pesar de ubicarse en una única localidad de las más de 100 muestreadas por nosotros, las investigaciones en curso podrían revelar pronto más citas de la especie en el país y el resto del continente. Se deben establecer políticas y procedimientos estrictos de aplicación de la ley en el comercio de especies acuáticas como medida preventiva para preservar la biodiversidad nativa.

Palabras clave: Especies exóticas invasoras; comercio de especies de acuario; hábitats dulceacuícolas; norte de África; Planorbidae.

Recibido/Received: 05/06/2022; Aceptado/Accepted: 11/10/2022; Publicado en línea/Published online: 16/05/2023

Cómo citar este artículo/Citation: Taybi, A.F., Glöer, P. & Mabrouki, Y. 2023. First record of the exotic seminole rams-horn Helisoma duryi (Wetherby, 1879), (Gastropoda: Planorbidae) in Morocco. Graellsia, 79(1): e181. https://doi.org/10.3989/graellsia.2023.v79.362

  1. Abstract
  2. Resumen
  3. Introduction
  4. Material and methods
  5. Results
  6. Discussion
  7. References


Invasive species are recognized as the second leading cause of extinctions around the world (‍Wilcove et al., 1998). In fact, some of these invasive exotic species have deeply impacted the environment, human health and the economy worldwide (‍Kettunen et al., 2008; ‍Mazza et al., 2014). In this regard, trade in aquarium and ornamental species is emerging as major source for species likely to invade aquatic habitats worldwide (‍Padilla & Williams, 2004). This trade moves thousands of species around the globe, opening the door to unwanted organisms being released into freshwater and marine ecosystems, with considerable adverse economic and ecological impacts (‍Taylor et al., 1984; ‍Mazza et al., 2015).

Despite their relatively small size and low mobility, some continental gastropods are defined as successful invasive species and have already drawn the attention of global specialists in the field of biological invasions (‍Vinarski et al., 2015). The acute bladder snail Physella acuta (Draparnaud, 1805) and the New Zealand mud snail Potamopyrgus antipodarum (J.E. Gray, 1843) are good examples of biological invaders in Class Gastropoda (‍Alonso et al., 2019; ‍Butkus et al., 2019). Another successful freshwater gastropod invader is Helisoma duryi (Wetherby, 1879), a medium-sized planorbid endemic to Florida (‍Baker, 1945) which has migrated from its native range to South America, Europe, Africa, and adjacent islands (‍Alexandrowicz, 2003; ‍Bank & Neubert, 2017; ‍Gherardi, 2007; ‍Glöer, 2019).

Helisoma duryi was first introduced in the African continent in South Africa and Namibia (‍Brown, 1967; ‍Appleton, 1977), to be recorded later in various other countries (‍Grano, 2022). In this paper, we report the first finding of an acclimated population of the exotic snail Helisoma duryi in Morocco. Moreover, we discuss the possible mechanisms of introduction and call for an increased awareness of the impacts associated with the aquarium trade in Morocco’s native freshwater fauna.

Material and methods[Up]

In order to promote knowledge on the freshwater molluscs of Morocco, several field expeditions have been conducted since 2014 in the northern part of the country. More than 100 localities have been investigated and most of these sampling sites were visited at least three times (e.g., ‍Taybi et al., 2017; ‍Mabrouki et al., 2020a for more details on the localities). Benthic invertebrate samples (including molluscs) were taken with a “Surber” sampler. The quantitative samples (of an order of eight) for the different microhabitats present on the site are taken against the current of water. The choice of microhabitats selected is based both on their biogenic capacity (favourable to aquatic life). The mainly qualitative benthic fauna samples were taken by nets, dip nets and forceps. For each sample, a first sorting was carried out on the field during which the fauna was preserved in a jar containing 70° alcohol. A second and finer sorting was performed in the laboratory under a binocular loupe in which all remaining macroinvertebrates were recovered and stored in 70° alcohol.

Water conductivity, pH, and dissolved oxygen were measured in situ with a multiparametric measuring device (WTW, Multi-Line P4). Other parameters (ammonium and BOD5 -Biological oxygen demand-) were measured in the laboratory. Photographs were made with a digital camera system (Leica Microscope M205C with digital camera Leica DMC5400). The map was made using ArcGIS software. Voucher specimens were deposited in the collections of the authors. Identifications were made using the identification key of Glöer (‍2019).


About thirty individuals of Helisoma duryi were collected in the Ain Talba spring and its emissary (34°32’41.0” N, 1°56’44.8” W), south Oujda, on 19/10/2021 and 20/02/2022 (Figs 12). The shell size of the collected juvenile specimens varied between 4 and 7 mm, whereas adult specimens reached a diameter of about 20 mm. The shells of Helisoma duryi are a pale, translucent brown colour. The 4.5 whorls are coiled in a plane, rapidly increasing, the left side is flat, and the right side is deeply umbilicated. These criteria distinguish it from the native Planorbidae species (‍Glöer, 2019).

The abundance of H. duryi was about 11 individuals per 0.5 m2. Helisoma duryi was found with different invertebrate aquatic species, including: Physella acuta (Draparnaud, 1805) (Gastropoda); Hygrotus confluens (Fabricius, 1787), Deronectes fairmairei Lepieur, 1876, Laccophilus hyalinus testaceus Aubé, 1837, Helochares lividus (Forster, 1771), and Laccobius atrocephalus atrocephalus Reitter, 1872 (aquatic Coleoptera); Caenis luctuosa (Burmeister, 1839) and Baetis sp. (Ephemeroptera, larvae); Corixa affinis Leach, 1817, Parasigara favieri (Poisson, 1939), Micronecta scholtzi (Fieber, 1860), Nepa cinerea Linnaeus, 1758 (aquatic Hemiptera); Anax imperator Leach, 1815, Orthetrum cancellatum (Linnaeus, 1758) and Crocothemis erythraea (Brullé, 1832) (Odonata, larvae and imagos); Mesophylax sp. (Trichoptera, larvae). The aquaticvertebrates comprised amphibians (Pelophylax saharicus (Boulenger in Hartert, 1913)), and aquatic reptiles (Natrix maura (Linnaeus, 1758) and Mauremys leprosa leprosa (Schweigger, 1812)).

The analysis of the physicochemical parameters of the water (ammonium and BOD5) revealed a good environmental quality of the habitat (Table 1), according to the Moroccan standards of the quality of the surface waters (SD).

Table 1.— Mean values of the physical and chemical water parameters measured at the sampling locality (Ain Talba and its emissary). M (Mean), SD (Standard deviation), Min (Minimum value), Max (Maximum value).

Tabla 1.– Valores medios de los parámetros físicos y químicos del agua medidos en la localidad de muestreo (Ain Talba y su emisario). M (Media), SD (Desviación estándar), Min (Valor mínimo), Max (Valor máximo).

Parameter pH Conductivity (mg∙L -1 ) Dissolved oxygen (mg∙L -1 ) Ammonium (mg∙L -1 ) BOD5 (mg∙L -1 )
M 7.9 650 7.5 0.03 1.5
SD 6.5–8.5 <1300 >5 <0.5 <5
Min 7 550 6.5 0.02 1
Max 8.2 750 8.5 0.04 2

Fig. 1.— Distribution and habitat of Helisoma duryi collected in Morocco.

Fig. 1.– Distribución y hábitat de Helisoma duryi recolectado en Marruecos.


Fig. 2.— The shell of Helisoma duryi collected in Morocco. A. Umbilical view. B. Apertural view. C. Apical view.

Fig. 2.– Concha de Helisoma duryi recolectada en Marruecos. A. Vista umbilical. B. Vista de apertura. C. Vista apical.



The Seminole rams-horn Helisoma duryi has successfully spread through the southwestern Palearctic (‍Glöer, 2019). Our finding provides the first record from Morocco and North Africa, increasing the known biodiversity of planorbid snails to six genera in Morocco (‍Mabrouki et al., 2022). The number of individuals of H. duryi collected was relatively low in this first study. This suggests the invasion could be in its initial stage, but further investigations could reveal more occurrences of the species in the country and the rest of the continent. The species seems to require habitats with good water quality, such as the waters of Ain Talba and its emissary, as judged by the Moroccan standards of the quality of the surface waters (‍Barakat et al., 2016; ‍Taybi et al., 2020a).

Regarding the introduction of H. duryi in Morocco, one of the most accredited hypotheses suggests an intentional release of this gastropod, which is a very popular ornamental snail among aquarists (‍Appleton, 1977; ‍Alexandrowicz, 2003; ‍Grano 2022). Helisoma duryi can be introduced into a new region through other mechanisms: escapes from artificial irrigation channels, reservoirs in parks, botanical gardens, fish farms and greenhouses (‍Alexandrowicz, 2003; ‍Vimpère, 2004). Intentional release may be related with its use as a biological control agent of schistosomiasis by controlling the populations of Bulinus O.F. Müller, 1781 (‍Appleton, 1977).

Biological invasions and the pathways of introduction and spread of alien species are not thoroughly documented in Morocco, but recently, an increasing number of invasive aquatic species has been documented (‍Mabrouki et al., 2019a, ‍2019b, ‍2021; ‍Taybi & Mabrouki 2020; ‍Taybi et al., 2020b, ‍2020c). The aquarium trade is increasingly considered as an important pathway for the introduction of freshwater alien aquatic species in the country. For example, it is the main route of introduction into freshwaters in Morocco of the mummichog Fundulus heteroclitus (Linnaeus, 1766), the green swordtail Xiphophorus hellerii Heckel, 1848, and for other successful freshwater gastropod invaders such as the New Zealand mudsnail Potamopyrgus antipodarum, the American limpet Ferrissia californica (Rowell, 1863), the Red-rimmed melania Melanoides tuberculata (O.F. Müller, 1774), and the acute bladder snail Physella acuta (‍Mabrouki et al., 2020b, ‍2023; ‍Taybi et al., 2017, ‍2020b, ‍2021).

Freshwater gastropod invasions through human help can bring huge impacts on the native biodiversity and many snail species have proved to be very successful invaders in the last years, able even to cross-oceans and continents (‍Karatayev et al., 2009; ‍Vinarski, 2017). With the continuous deterioration in water quality of the freshwater ecosystems, acting synergically with the effects of global warming can potentially favour the expansion of H. duryi in Morocco or North Africa as a whole. Therefore, monitoring the presence and expansion of the species within invaded areas and studies improving our biological and ecological knowledge of the species are crucial to mitigate their possible impact on native communities.



Alexandrowicz, S. W. 2003. Planorbella duryi (Wetherby, 1879) from the Crater-Lake Albano (Central Italy). Folia Malacologica, 11(3/4): 89–93. https://doi.org/10.12657/folmal.011.009


Alonso, Á., Castro-Díez, P., Saldaña-López, A. & Gallardo, B. 2019. The New Zealand mud snail Potamopyrgus antipodarum (J.E. Gray, 1853) (Tateidae, Mollusca) in the Iberian Peninsula: temporal patterns of distribution. BioInvasions Records, 8(2): 287-300. https://doi.org/10.3391/bir.2019.8.2.11


Appleton, C. C. 1977. The exotic fresh-water snail Helisoma duryi (Wetherby, 1879) (Planorbidae) in Southern Africa. Zoologische Mededelingen, 52 (10): 125-‍135.


Baker, F. C. 1945. The molluscan family Planorbidae. The University of Illinois Press. Urbana, Ill. Xxxvi + 530 pp.


Bank, R. & Neubert, E. 2017. MolluscaBase. Checklist of the land and freshwater Gastropoda of Europe. Last update: 16/07/2017. 170 pp.


Barakat, A., El Baghdadi, M., Rais, J., Aghezzaf, B. & Slassib M. 2016. Assessment of spatial and seasonal water quality variation of Oum Er Rbia River (Morocco) using multivariate statistical techniques. International Soil and Water Conservation Research, 4: 284–292. https://doi.org/10.1016/j.iswcr.2016.11.002


Brown, D.S. 1967. Additional notes on South African introduced molluscs, including a species new to the list. Annals of the Natal Museum, 18: 501–504.


Butkus, R., Višinskienė, G. & Arbačiauskas, K. 2019. First record of the acute bladder snail Physella acuta (Draparnaud, 1805) in the wild waters of Lithuania. BioInvasions Records, 8(2): 281–286, https://doi.org/10.3391/bir.2019.8.2.10


Gherardi F., 2007. Biological invaders in inland waters: Profiles, distribution, and threats. Springer Science & Business Media. https://doi.org/10.1007/978-1-4020-6029-8


Glöer P. 2019. The freshwater gastropods of the West Palaearctic. Vol. 1: Fresh- and brackish waters except spring and subterranean snails. Identification Key, Anatomy, Ecology, Distribution. Biodiversity Research Lab. Hetlingen. 399 pp.


Grano, M. 2022. The non-indigenous freshwater molluscs, and particularly Helisoma scalare (Jay, 1839) (Gastropoda Planorbidae), of Lake Albano (Rome, Italy). Biodiversity Journal, 13 (1): 281–291. https://doi.org/10.31396/Biodiv.Jour.2022.


Karatayev, A.Y., Burlakova, L.E. & Karatayev, V.A. 2009. Introduction, distribution, spread, and impacts of exotic freshwater gastropods in Texas. Hydrobiologia, 619: 181–194. https://doi.org/10.1007/s10750-008-9639-y


Kettunen, M., Genovesi, P., Gollasch, S., Pagad, S., Starfinger, U., ten Brink, P. & Shine, C. 2008. Technical support to EU strategy on invasive species (IAS) - Assessment of the impacts of IAS in Europe and the EU (final module report for the European Commission). Institute for European Environmental Policy (IEEP). Brussels. 44 pp. + Annexes.


Mabrouki, Y., Ben Ahmed R., Taybi, A.F. & Rueda, J. 2019a. Annotated checklist of the leech (Annelida: Hirudinida) species of the Moulouya river basin, Morocco with several new distribution records and an historical overview. African Zoology, 54(4): 199–214. https://doi.org/10.1080/15627020.2019.1671218


Mabrouki, Y., Taybi, A. F., Skalli, A. & Sánchez-Vialas, A. 2019b. Amphibians of the Oriental Region and the Moulouya River Basin of Morocco: distribution and conservation notes. Basic and Applied Herpetology, 33: 19-32. https://doi.org/10.11160/bah.134


Mabrouki, Y., Taybi, A. F., El Alami, M., Wiggers R. & Berrahou, A. 2020a. New data on fauna of caddisflies (Insecta: Trichoptera) from northeastern Morocco with notes on chorology. Aquatic Insects, 41(4): 356-390. https://doi.org/10.1080/01650424.2020.1797817


Mabrouki, Y., Taybi, A. F., Bahhou, J. & Doadrio, I. 2020b. The first record of the green swordtail Xiphophorus helleri (Miller, 1966) (Poeciliidae) established in the wild from Morocco. Journal of Applied Ichthyology, 36(6): 1-6. https://doi.org/10.1111/jai.14105


Mabrouki, Y., Crocetta F. & Taybi, A.F. 2021. First Record of Branchiomma luctuosum (Grube, 1870) (Annelida: Polychaeta: Sabellidae) in Morocco. Thalassas: An International Journal of Marine Sciences, 37(5): 717-720. https://doi.org/10.1007/S41208-021-00348-7


Mabrouki, Y., Glöer, P. & Taybi, A.F. 2022. Gyraulus marocana sp. nov., a new freshwater snail species (Mollusca, Gastropoda, Planorbidae) from Morocco. Nature Conservation Research, 7(1): 96-100. https://doi.org/10.24189/ncr.2022.007


Mabrouki, Y., Glöer, P. & Taybi, A.F. 2023. The first record of the North American freshwater limpet Ferrissia californica (Mollusca, Gastropoda) in Morocco. Nature Conservation Research, 8(1): 108-112. https://doi.org/10.24189/ncr.2023.004


Mazza, G., Tricarico, E., Genovesi, P. & Gherardi, F. 2014. Biological invaders are threats to human health: an overview. Ethology, Ecology and Evolution 26(2–3): 112–129. https://doi.org/10.1080/03949370.2013.863225


Mazza, G., Aquiloni, L., Inghilesi, A. F., Giuliani, C., Lazzaro, L., Ferretti, G., Lastrucci, L., Foggi, B. & Tricarico, E. 2015. Aliens just a click away: the online aquarium trade in Italy. Management of Biological Invasions, 6(3): 253–261. https://doi.org/10.3391/mbi.2015.6.3.04


Padilla, D.K. & S. L. Williams, 2004. Beyond ballast water: aquarium and ornamental trades as sources of invasive species in aquatic ecosystems. Frontiers in Ecology and the Environment, 2(3): 131–138. https://doi.org/10.1890/1540-9295(2004)002[0131:BBWAAO]2.0.CO;2


Taybi, A.F. & Mabrouki, Y. 2020. The American blue crab Callinectes sapidus Rathbun, 1896 (Crustacea: Decapoda: Portunidae) is rapidly expanding through the Mediterranean coast of Morocco. Thalassas: An International Journal of Marine Sciences, 36(2): 1-5. https://doi.org/10.1007/s41208-020-00204-0


Taybi, A.F., Mabrouki, Y., Chavanon, G., Millán, A. & Berrahou, A. 2017. New data on aquatic beetles of Morocco (Coleoptera Adephaga: Gyrinidae, Haliplidae and Dytiscidae). Baltic Journal of Coleopterology, 17(1): 83–106.


Taybi, A. F., Mabrouki, Y., Berrahou, A. & Legssyer B. 2020a. Spatio-temporal typology of the physicochemical parameters of the Moulouya and its main tributaries. African Journal of Aquatic Sciences, 45(4): 431–441. https://doi.org/10.2989/16085914.2020.1727832


Taybi, A. F., Mabrouki, Y. & Doadrio, I. 2020b. The occurrence, distribution and biology of invasive fish species in fresh and brackish water bodies of NE Morocco. Arxius de Miscellania Zoologica, 18: 59-73. https://doi.org/10.32800/amz.2020.18.0059


Taybi, A. F., Mabrouki, Y., Chavanon, G. & Millán, A. 2020c. The alien boatman Trichocorixa verticalis verticalis (Hemiptera: Corixidae) is expanding in Morocco. Limnetica, 39(1): 49-59. https://doi.org/10.23818/limn.39.04


Taybi, A.F., Mabrouki, Y. & Glöer, P. 2021. First record of the New Zealand Mudsnail Potamopyrgus antipodarum (J.E. Gray, 1843) (Tateidae, Mollusca) in Africa. Graellsia, 77(2): e140. https://doi.org/10.3989/graellsia.2021.v77.303


Taylor, J.N., Courtenay Jr., W.R. & McCann, J.A. 1984. Knows impacts of exotic fishes in the continental United States. In: W.R. Courtenay Jr. and J.R. Stauffer Jr. (eds.). Distribution, biology, and management of exotics fishes. The Johns Hopkins University Press, Baltimore, MD: 322-‍327.


Vimpère, J. 2004. Introduction en France continentale d’un gastéropode d’eau douce originaire de Floride: Planorbella duryi (Wetherby, 1879) (Mollusca: Gastropoda: Pulmonata). Le Naturaliste Vendéen, 4: 127–130.


Vinarski, M. 2017. The history of an invasion: phases of the explosive spread of the physid snail Physella acuta through Europe, Transcaucasia and Central Asia. Biological Invasions, 19(4): 1299–1314. https://doi.org/10.1007/s10530-016-1339-3


Vinarski, M.V., Andreev, N.I., Andreeva, S.I., Kazantseu, I.E., Karimov A.V. & Lazutkina, E.A. 2015. Alien mollusk species in the aquatic ecosystems of Western Siberia: a review. Russian Journal of Biological Invasion, 6: 137–147. https://doi.org/10.1134/s2075111715030078


Wilcove, D.S., Rothstein, D., Dubow, J., Phillips, A. & Losos, E. 1998. Quantifying threats to imperiled species in the United States. BioScience 48: 607–615. https://doi.org/10.2307/1313420