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Logotyp för Naturhistoriska riksmuseet
Logotyp för Naturhistoriska riksmuseet
Microcotyle isyebi

Microcotyle isyebi is found on the gills of the bluespotted seabream Pagrus caeruleostictus, a high‐priced sparid fish. Photo by Chahinez Bouguerche.

Systematics and integrative taxonomy of Monogenea parasitising Swedish fish species

Every marine organism is potentially a host to a parasite, according to season and nearby environment. Within flatworms, the classes Monopisthocotylea and Polyopisthocotylea have veterinary and economic importance as they are typically hosted by fishes and feed on their blood or epithelium. Despite their immense species richness, only a fraction of their diversity has been documented, underlining the pressing need to explore their global biodiversity.

Forskningsområden: Zoologi

Forskningsämnen: Monogenea, Parasiter, Fiskparasiter, Monopisthocotylea, Polyopisthocotylea, Plattmaskar


Monopisthocotylea and Polyopisthocotylea (previously known as Monogenea) are classes of ecologically and economically significant platyhelminth parasites of freshwater and marine hosts. Common in many seas, their presence in a range of cultured species has been responsible for mortality or a reduction in health. Although these classes are remarkably species-rich groups, only a small proportion of their diversity has been described. Their biodiversity is estimated to 25,000 species with only a fraction currently described (3,000–4,000). It has been suggested that the distribution of these parasites does not reflect their geographical distribution but more the concentrations of taxonomic efforts.

The current project targets relevant questions of the global biodiversity of parasitic Monopisthocotylea and Polyopisthocotylea, using integrative taxonomy as a first attempt to evaluate the “monogenean” fauna of Swedish fish species. Morphological and molecular data of these parasitic platyhelminths from the northeast Atlantic and the Baltic Sea will be important for the global phylogeography, distribution and the phylogeny of the two groups.

Project description

The aim of this project is to provide a systematic study of monopisthocotylean and polyopisthocotylean flatworms parasitising fish species from Swedish waters, by documenting species new for the fauna of Sweden and describing species new to science.

As the number of expected species of Monopisthocotylea and Polyopisthocotylea per species of fish is 3-5 and given the estimated 140 fish species known in Sweden, it is expected that there are about 420 to 700 different parasitic species in Swedish fishes. The total diversity is likely 4-7 times the currently reported number of species. This project will provide thoroughly identified data of monopisthocotylean and polyopisthocotylean parasites including DNA barcodes and illustrations of diagnostic features vital for identification keys.

Another topic of particular interest is exploring museum collections for a better assessment of the biodiversity of monopisthocotylean and polyopisthocotylean parasites. These fish parasites are known for being subject to seasonal population dynamics with significant differences in the prevalence rates and peaks in certain seasons. Hence, the absence of parasites, while advantageous for the host, may temporarily result in missed opportunities to contribute to a better understanding of poorly known parasitic species. Fortunately, natural history museums house billions of relevant specimens accumulated over centuries, offering an exceptional potential for harvesting a parasitological dataset for taxonomical studies and various other purposes. These collections provide cost-free access, significantly reducing typical expenses related to travel, consumable supplies, and field excursions and are continually used for comparative studies in our project.


Swedish Taxonomy Initiative

Institut de Systématique, Évolution, Biodiversité, Muséum national d'Histoire naturelle External link., Paris, France

Selected publications

Cappelletti, A., Bouguerche, C. 2024. “Something old, something new, something borrowed, and the oioxeny is true”: description of Plectanocotyle jeanloujustinei n. sp. (Polyopisthocotylea, Plectanocotylidae) from the MNHN Helminthology collection with novel molecular and morphological data for P. gurnardi (Van Beneden & Hesse, 1863) (sensu stricto) from Sweden. International Journal for Parasitology: Parasites and Wildlife, 23, 100914. External link.

External participants

Jean-Lou Justine External link., Institut de Systématique, Évolution, Biodiversité, Muséum national d'Histoire naturelle, Paros, France

Romain Gastineau External link., Institute of Marine and Environmental Sciences, University of Szczecin, Szczecin, Poland

Anti Vasemägi External link., Department of Aquatic Resources, Swedish University of Agricultural Sciences, Stångholmsvägen, Sweden

Kennet Lundin External link., Department of Marine Sciences, University of Gothenburg/ Gothenburg Museum of Natural History, Gothenburg, Sweden

Project Manager

Chahinez Bouguerche




Resarch Areas: Zoology

Research Subjects: Monogenea, Monopisthocotylea, Polyopisthocotylea, Flatworms