Limnetica, 40(1): 57-78 (2021). DOI: 10.23818/limn.40.05 © Asociación Ibérica de Limnología, Madrid. Spain. ISSN: 0213-8409 Redescription of Acanthocyclops vernalis (Fischer, 1853) and Acanthocyclops robustus (Sars, 1863) from neotypes, with special reference to their distinction from Acanthocyclops americanus (Marsh, 1892) and its invasion of Eurasia Victor R. Alekseev1,*, Maria R. Miracle2,†, Maria Sahuquillo2,3 and Eduardo Vicente2 1 Zoological Institute of the Russian Academy of Sciences, Universitetskaya Embankment 1, St Petersburg 199034, Russia. 2 Department of Microbiology and Ecology, ICBiBE, University of Valencia, 46100 Burjassot, Valencia, Spain. 3 Subdirecció General del Medi Natural, Generalitat Valenciana, València, Spain. † Deceased * Corresponding author: [email protected] Received: 02/04/19 Accepted: 08/01/20 ABSTRACT Redescription of Acanthocyclops vernalis (Fischer, 1853) and Acanthocyclops robustus (Sars, 1863) from neotypes, with special reference to their distinction from Acanthocyclops americanus (Marsh, 1892) and its invasion of Eurasia This paper provides a redescription of Acanthocyclops vernalis and A. robustus neotypes collected in their type localities in Russia (Orlov pond, Peterhof) and Norway (a stream outcoming from a lake in Oslo) with a special attention to their morphologi- cal differentiation from A. americanus. Due to overmixing of these species throughout most of the last century and fast arrival and spreading of the aggressive planktonic predator A. americanus, all previous indications of A. robustus should be checked and confirmed. More than 200 localities in Valencia region (Spain) and more than 30 localities in Armenia, Belgium, Egypt, Finland, France, Kazakhstan, Norway, Russia, Sweden and Tunisia were checked for the presence of A. americanus. In all these countries the invader was found in large numbers as dominant species often substituting other native Acanthocyclops species in limnetic communities. A brief history and possible explanation of the successful invasion of A. americanus in Eurasia is discussed. Key words: Acanthocyclops robustus; Acanthocyclops vernalis; Acanthocyclops redescriptions; cyclopoid taxonomy; Acanth- ocyclops americanus; biological invasion, distribution in Eurasia RESUMEN Redescripción de los neotipos de Acanthocyclops vernalis (Fischer, 1853) y Acanthocyclops robustus (Sars, 1863), con especial atención a sus diferencias morfológicas con Acanthocyclops americanus (Marsh, 1892) y su invasión en Eurasia Este trabajo proporciona una nueva descripción de los neotipos de A. vernalis y A. robustus recopilados en sus localidades tipo en Rusia (estanque de Orlov, Peterhof) y Noruega (una corriente que sale de un lago en Oslo), con especial atención a su diferenciación morfológica respecto a A. americanus. Debido a la mezcla de estas especies prácticamente durante todo el siglo pasado y la rápida llegada del agresivo depredador planctónico A. americanus, todas las indicaciones anteriores de presencia de A. robustus deben verificarse y confirmarse. Se estudia la presencia de A. americanus en más de 200 localidades en la región de Valencia (España) y más de 30 ubicaciones en Armenia, Bélgica, Egipto, Finlandia, Francia, Kazajstán, Noruega, Rusia, Suecia y Túnez. En todos estos países, la especie invasora se encontró en grandes cantidades y como forma dominante, a menudo sustituyendo a las especies nativas de Acanthocyclops en las comunidades limnéticas. También se presenta una breve historia y posible explicación de la exitosa invasión de A. americanus en Eurasia. Palabras clave: Acanthocyclops robustus; Acanthocyclops vernalis; redescripción de Acanthocyclops; taxonomía de ciclópi- dos; Acanthocyclops americanus; invasión biológica, distribución en Eurasia Redescription of Acanthocyclops vernalis (Fischer, 1853) and Acanthocyclops robustus (Sars, 1863) from neotypes, with special reference to their distinction from Acanthocyclops americanus (Marsh, 1892) and its invasion of Eurasia Victor R. Alekseev1,*, Maria R. Miracle2,†, Maria Sahuquillo2,3 and Eduardo Vicente2 1 Zoological Institute of the Russian Academy of Sciences, Universitetskaya Embankment 1, St Petersburg 199034, Russia. 2 Department of Microbiology and Ecology, ICBiBE, University of Valencia, 46100 Burjassot, Valencia, Spain. 3 Subdirecció General del Medi Natural, Generalitat Valenciana, València, Spain. † Deceased * Corresponding author: [email protected] Received: 02/04/19 Accepted: 08/01/20 ABSTRACT Redescription of Acanthocyclops vernalis (Fischer, 1853) and Acanthocyclops robustus (Sars, 1863) from neotypes, with special reference to their distinction from Acanthocyclops americanus (Marsh, 1892) and its invasion of Eurasia This paper provides a redescription of Acanthocyclops vernalis and A. robustus neotypes collected in their type localities in Russia (Orlov pond, Peterhof) and Norway (a stream outcoming from a lake in Oslo) with a special attention to their morphologi- cal differentiation from A. americanus. Due to overmixing of these species throughout most of the last century and fast arrival and spreading of the aggressive planktonic predator A. americanus, all previous indications of A. robustus should be checked and confirmed. More than 200 localities in Valencia region (Spain) and more than 30 localities in Armenia, Belgium, Egypt, Finland, France, Kazakhstan, Norway, Russia, Sweden and Tunisia were checked for the presence of A. americanus. In all these countries the invader was found in large numbers as dominant species often substituting other native Acanthocyclops species in limnetic communities. A brief history and possible explanation of the successful invasion of A. americanus in Eurasia is discussed. Key words: Acanthocyclops robustus; Acanthocyclops vernalis; Acanthocyclops redescriptions; cyclopoid taxonomy; Acanth- ocyclops americanus; biological invasion, distribution in Eurasia RESUMEN Redescripción de los neotipos de Acanthocyclops vernalis (Fischer, 1853) y Acanthocyclops robustus (Sars, 1863), con especial atención a sus diferencias morfológicas con Acanthocyclops americanus (Marsh, 1892) y su invasión en Eurasia Este trabajo proporciona una nueva descripción de los neotipos de A. vernalis y A. robustus recopilados en sus localidades tipo en Rusia (estanque de Orlov, Peterhof) y Noruega (una corriente que sale de un lago en Oslo), con especial atención a su diferenciación morfológica respecto a A. americanus. Debido a la mezcla de estas especies prácticamente durante todo el siglo pasado y la rápida llegada del agresivo depredador planctónico A. americanus, todas las indicaciones anteriores de presencia de A. robustus deben verificarse y confirmarse. Se estudia la presencia de A. americanus en más de 200 localidades en la región de Valencia (España) y más de 30 ubicaciones en Armenia, Bélgica, Egipto, Finlandia, Francia, Kazajstán, Noruega, Rusia, Suecia y Túnez. En todos estos países, la especie invasora se encontró en grandes cantidades y como forma dominante, a menudo sustituyendo a las especies nativas de Acanthocyclops en las comunidades limnéticas. También se presenta una breve historia y posible explicación de la exitosa invasión de A. americanus en Eurasia. Palabras clave: Acanthocyclops robustus; Acanthocyclops vernalis; redescripción de Acanthocyclops; taxonomía de ciclópi- dos; Acanthocyclops americanus; invasión biológica, distribución en Eurasia 58 Alekseev et al. 59 INTRODUCTION cyclopid population which is not enough nowa- between them and A. americanus or some other MATERIALS AND METHODS days when molecular-genetic tools have clearly similar species of Acanthocyclops. Acanthocycops americanus (Marsh, 1892) a corroborated that the morphologically different This paper provides a redescription of A. 1.- Morphological description of A. ameri- planktonic cyclopid first described from the populations belong to the same species. Even vernalis and A. robustus from the type localities canus Great Lakes in Northern America was found excellent morphologists in XXI century cannot with a special attention to differentiation from A. soon after by Lowndes (1926, 1928a) in Great ignore results of molecular-genetic species americanus. In addition, we provide new Morphological description of A. americanus had Britain and later on in several other countries of validation that was confirmed for this Acantho- ecological features on A. americanus biology been done on material from terra typica, obtained the Old World (Dussart, 1967; Monchenko, cyclops robustus - vernalis complex recently and current distribution based, first, on exten- from Prof. Stainly Dodson, Wisconsin USA (Mir- 1961; Alekseev & Kosova, 1976). It became the (Błędzki & Rybak, 2016). A good example could sive European samplings and, second, on inten- acle et al., 2013). Hereafter we have used neotype first documented invasive copepod species be found in Cyclops abyssorum group: many sive and detailed samplings over a single Medi- specimens of two morphologically close species transported from the Americas to Europe. In the local populations of this group were described as terranean area, Valencia region, as a case study. which consist of: 10 ♂ and 20 ♀ of A. vernalis last century it was also found in limnetic com- separate species but in direct hybridization Both based on collection from authors and using selected from a sample taken in April 1998 in munities throughout Eurasia. After Kiefer’s experiment of Einsle (1996) easily crossed with the morphological differentiation detailed in the Orlov pond,