Checklist of the Cestoda (Platyhelminthes) of Switzerland

Abstract: A checklist, including all the cestode taxa recorded from Switzerland, their hosts, as well as deposited specimens available in scientific collections, is provided. The country has one of the richest European cestode faunas consisting of 251 species, almost all of them cyclophyllideans, that were identified in 190 vertebrate and 24 invertebrate host species. This is a very significant increase over the previous similar list that was established one century ago by Fuhrmann (1926). Since then, advances have been particularly important for parasites of mammals and birds although an important margin of progress remains for the latter as several bird families have been surprisingly little studied in the country. A large proportion of species described in Switzerland, including 22 that are represented by types, are available in public collections, most of them at the Muséum d'histoire naturelle de Genève. New reports were numerous in the second half of last century but have become scarce in recent decades. Today, tapeworms have been identified in no more than one third of Swiss vertebrate species and despite one century of progress, the true diversity of this fauna in the country remains to be determined.

unfashionable.The last significant reports in this field in Switzerland are from the late 1980s (Szelenbaum-Cielecka et al., 1988).The last two new cestode species descriptions from Swiss vertebrates, one in very common Song Thrushes and one in Great crested Grebes, are respectively over 30 and 20 years old (Gigon & Beuret, 1991;Vasileva et al., 2000).

Sources:
1) Museum data.Muséum d'histoire naturelle de Genève (MHNG) holds one of the major collections of cestodes worldwide (>22'000 lots), including most historic collections of Swiss cestodologists.Its catalogue provided the backbone of the present list.
Additional data were requested from other Swiss Museums that maintain scientific collections as well as from major foreign Museums likely keeping Swiss specimens.2) Other institutions data.Some veterinary or paramedical institutions in Switzerland were asked for archives or registers.3) Bibliography.Searches were made with appropriate taxonomical and geographical filters in Web of Science's Zoological Record (© Clarivate).4) Several unpublished student works from parasitology departments in Swiss institutes.

Conditions for listing:
For a species to be included in the checklist, at least one of two nonexclusive conditions had to be met: The taxon had to be published with an explicit mention of its Swiss origin and/or specimens labeled as of Swiss origin had to be registered in collections in an academic institution.
For the sake of consistency, and contrary to Fuhrmann (1926), observations from bordering foreign localities (e.g., "Salève" or "Black Forest") are not included here, leading to the exclusion of a few taxa that were listed in Fuhrmann's catalogue.

Data provided (Table 1, Annex 1):
Cestodes specific identification (generic in a few cases): Except in rare instances, identifications have not been checked.Thus, the original publication/label name is reported, either as the valid or synonym name of the taxon.A synonym list is provided but does not aim at comprehensiveness: only names that have been used when specifically referring to specimens in Switzerland are mentioned.
Hosts: All hosts, both final and intermediate, belonging to the Swiss fauna are reported.
For vertebrates, hosts are listed under their present taxonomic status according to Fishbase (Froese & Pauly, 2021), Amphibian Species of the World (Frost, Switzerland.This list includes the names of the parasites, their known hosts, a simplified distribution in the country, a selective bibliography as well as a list of the known specimens kept in scientific institutions. It should be emphasized that such a compilation is not a taxonomic work.As far as possible, historic names of parasites are listed under their presently accepted synonymy and they are placed in the most recent higher systematics of the group (Caira & Jensen, 2017), however no nomenclatural act is made here.This checklist aims at being a practical reference and tool for researchers and other users of biodiversity information.

HISTORICAL CONTEXT
The earliest report of an identifiable parasitic worm in Switzerland seems to be that of Diphyllobothrium latum by Dunus (1592).It was followed by a few publications in the 17th century on parasites of humans.Later reports became more common but remained mostly limited to common parasites of domesticated animals until the mid-19th century when a more diverse and steady flux of publications started.A rather large spectrum of authors has contributed to the knowledge of the Swiss fauna, but only a few have built a consistent body of work.The most important of them being Friedrich Zschokke (1860Zschokke ( -1936) ) in Basel, who published essentially on parasites of fish; Bruno Galli-Valerio (1867-1943) in Lausanne, veterinarian and physician, who probably examined the largest diversity of Swiss vertebrates through numerous publications (see Gaschen, 1950); Otto Fuhrmann (1871Fuhrmann ( -1945) ) in Neuchâtel, one of the giants of cestodology, who worked on most tapeworm groups and contributed significantly to the knowledge of Swiss Cyclophyllidea; Bernd Hörning (1931Hörning ( -2012) ) in Bern, a veterinarian with interest in many wild animals (see in particular: Hörning, 1963); and Claude Vaucher (1942-) in Geneva, who decisively contributed to the knowledge of the helminthofauna of micromammals.
Besides parasites of domestic animals (and humans), the focus of cestodes biodiversity research in Switzerland long concentrated on parasites of fish from the country's major lakes, resulting in plethoric, and often repetitive, observations, especially at the turn of the 20th century.These are particularly problematic when considering the extremely complex fish diversity in Alpine lakes (see below).Works by K. Wolffhügel (1869Wolffhügel ( -1951) ) or Fuhrmann then progressively expanded our knowledge of the bird fauna, but a new focus on wild mammals only appeared in the 1960s.However, the latter two classes of vertebrates remain relatively poorly known, with significant gaps for example in passerines, or in chiropterans.As for amphibians and reptiles, only a very few isolated publications exist.Reports from larval forms in invertebrates are also limited and mostly ancient, as research on life cycles progressively became 2021), The Reptile Database (Uetz & Etzold, 1996), Avibase (Lepage, 2018), and Aulagnier et al. (2008) respectively for fish, amphibians, reptiles, birds and mammals (all online references accessed in 2021).Ancient host names have been updated in accordance.Parasites of captive hosts not belonging to the Swiss fauna are not listed.
The Swiss vertebrate fauna is well known, and most names are unambiguous.A significant exception to this statement concerns the fish, and especially the whitefishes (Coregonus spp., Salmonidae).Over the years, a very large number of names, both scientific and vernacular, have been used for these fish, especially in Swiss lakes.This is due to a complex history of speciation, colonization, hybridization, human transfers, and local extinctions.Revisions and descriptions of new taxa have been numerous (e.g., Selz et al., 2020).Up to 35 species may presently be living in Swiss lakes, but revisions keep diverging both in the number and names of these taxa.Despite several attempts to clarify their systematic status (e.g., Steinmann, 1950;Kottelat & Freyhof, 2007) no taxonomical consensus presently exists.Even the species concept best adapted to Coregonus taxa is not clear as so called "speciation reversals" seem to be the norm under changing ecological conditions (Vonlanthen et al., 2012).The problem is further enhanced when trying to match often partial or imprecise historical observations to present day nomenclature, a close to impossible task.Hence, I chose to retain the limited number of Coregonus species names that are recognized as valid in Fishbase (Froese & Pauly, 2021) even though this can lead to some inconsistencies.For example, in Lake Geneva, historical species are now considered extinct (Vonlanthen et al., 2012), but I nevertheless use their names, as in the original publications, as no consensus exists on other ones.It is most likely that each significant water body in the country hosts its own fish population/parasite population fauna (with possible speciation for either or both in some cases), but no convenient nomenclatural system, neither for hosts nor for parasites, has yet been accepted to adequately represent this situation.
In addition, some rare ambiguities may occur for reports from domestic mammals that have a wild conspecific in the country, in particular for cats, with both Felis s. silvestris and F. s. catus living in Switzerland.Unless specified otherwise, reports are assumed to be from the domesticated form.
Developmental stage: Hosts of larval forms are mentioned as such.Note that in a few cases both adult and larval worms can be found in the same host.
Localities: Detailed localities are not reported (and, most often, not available); only cantons and large water bodies are mentioned when such information exists.In some cases, especially for collection specimens, only the mention "Switzerland" is available, resulting in this field being kept empty.Cantons and water bodies mentioned might in some cases refer to the same observation from different sources.Standard Swiss cantons abbreviations (https://www.iso.org/obp/ui/#iso:code:3166:CH) are used, except for BA (Basel) being used as a collective for BL and BS (Basel state and Basel city).The main water bodies are abbreviated as follows: A: Lake Maggiore; B: Lake Biel/ Bienne; L: Lake Geneva/Léman; M: Lake Morat; N: Lake Neuchâtel; O: Lake Constance/Bodensee; T: Lake Thun; U: Lake Zug; V: Lake Lucerne/Vierwaldstättersee; Z: Lake Zürich.In a few cases CH is used for a documented countrywide distribution.
Collection dates: Only unambiguously reported collection years (which can significantly differ from publication dates) are mentioned.In most cases, especially for more ancient records, this information is lacking.
References: Bibliographic references are not listed exhaustively.A subjective selection of the most relevant publications citing the taxon is mentioned.For many specimens in collections, no associated publication is known.
Specimens: All databased specimens I am aware of are listed here with their accession number, and type status where appropriate.There are, however, a few unregistered samples from the large common species (Taenia, Diphyllobothrium, Ligula, …) on display, or in the collections, of many smaller institutions.

RESULTS
Mentions of at least 251 cestode species [in 125 genera and 21 families] forming 689 host/parasites pairs could be traced in Switzerland (including 5 species inquirendae) (Tables 1, 3).This is, respectively, a 99 and 132% increase on Fuhrmann's (1926) list.The main cestode order present in Switzerland is, by far, the Cyclophyllidea (218 spp.or 87% from total) with Hymenolepididae (111 spp.) followed by Dilepididae (36 spp.) as the most represented families.Altogether 214 species of hosts, 24 invertebrates and 190 vertebrates, have been recorded harboring cestode parasites.The cestode fauna of birds is the most diversified (Table 2).Eight species are known only from their metacestodes.Specimens from 208 (84%) of the species known from Switzerland are preserved in academic institutions, including 6 holotypes, 1 lectotype, 14 syntypes, 15 paratypes and 2 "types" specimens/lots representing 22 cestode species.These are distributed in 1250 lots, over 93% of them kept in the Muséum d'histoire naturelle de Genève (Annex 1).About 82% of the specimens with associated collection data were gathered in the second half of the last century.Parasites were recorded from all over Switzerland, although with a marked bias toward the Southern Alpine and Western parts of the country (Table 1).[4] As Taenia blanchardi in Fuhrmann (1926).
[21] These records are suspicious as rodents are normal intermediate hosts of V. mustelae.
[23] According to Wicht (2008) [28] A recent molecular analysis (Brabec et al., 2023) suggested, however, that P. fallax may be a valid species parasite in Coregonus sp. while P. longicollis would be restricted to Salmo spp.hosts.
[29] P. percae is a parasite of Perca fluviatilis and Esox lucius (postcyclic).Proteocephalus ocellatus (Rudolphi, 1802) was not recognized by Fuhrmann (1926) and is considered a synonym of P. percae (Muller, 1780) by Scholz & Hanzelova (1999).The numerous mentions of "P.ocellatus" in fish of other families, mostly in old records (e.g., Zschokke, 1884;Nufer, 1905)  As no further reports of these taxa have been published, their presence in the country remains uncertain.• Fuhrmann (1926) similarly reports the presence of Diplophallus polymorphus in Recurvirostra avosetta in Basel.A possible match for this material could be MHNG-PLAT-55673 that originates from the University of Neuchâtel collection, although no locality is mentioned on the label.Furthermore, the specimens, originally reported by Wolffhügel (1900), come from a "Zoologischer Garten von der Nordsee".In consequence this taxon has most likely not been found in Switzerland and I haven't considered it in the table.• An occurrence of Grillotia erinaceus (van Beneden, 1858) is mentioned in Lota lota in the early literature (e.g., Zschokke, 1903;Fuhrmann, 1926).Both the freshwater host and the locality (Lake Geneva) of this single record are highly improbable for a trypanorhynch cestode.No material is known.I have removed this host-parasite occurrence from the list.1911] is registered from Switzerland in the USNM (#1349984).Origins of this material are unclear, but the species is from the Neotropics and does not belong to the Swiss fauna.• Some data of Vaucher (1971) are difficult to interpret as a detailed host-parasite list by locality is not given.Geographical locations were ascertained on labels linked to specimens when available.In a few cases I considered that the parasite was present in Switzerland in each of its reported hosts whose distribution encompassed the country.

Sources
It should be noted that an important part of the data collected in this work comes from natural history collections material, highlighting the crucial importance of these institutions for our understanding of the biodiversity through time.Given their highly specialized nature, only a few museums maintain scientific collections of tapeworms and therefore I assume that a very high proportion of the existing information could be accessed.
A similar level of confidence could also be reached for published information through the rich bibliographic database of the MHNG library and bibliographic software.A few host/parasite reports were nevertheless difficult to track, especially when published in very local veterinary journals and a few have certainly been missed.Globally, though, I am confident that the information gathered in Table 1 is comprehensive.In addition to these traditional sources, a single occurrence of an ususual and quite unexpected host-parasite association was revealed through DNA sequencing (Taenia martis in H. sapiens, see Table 1).This is not surprising as only few sequences of cestodes of Swiss origin, mostly from Taeniidae and Proteocephalidae, are available in Genbank.

Available material
It is remarkable that a very high proportion (84%) of the species known from Switzerland are represented by at least one sample in academic institutions (Annex 1).This is the direct consequence of the intense activity of researchers at the University of Neuchâtel during most of the last century.Their collections (as well as samples entrusted to them) were ultimately kept at the museum of natural history of this city, then transferred to the MHNG, which became a major repository for helminthological collections.Interestingly, only 22 species from this large pool are represented by types.These types are mostly from parasites of micromammals and have almost all been published either by Baer and collaborators in the 30s or by recent authors (e.g., Makarikov & Kontrimavichus, 2011).No parasites from birds were described in the country since Vasileva et al. (2000).Some material may have been registered without mention of their type status and it is possible, although unlikely, that other taxa from Swiss origin have been described without clear reference in foreign publications with their types conserved in collections not surveyed herein.Nevertheless, potential candidates for Swiss endemics should be looked for within those 22 species, especially amongst the micromammal parasites.

Host coverage
In comparison with Fuhrmann (1926) a significantly higher proportion of the Swiss fauna is currently known to host cestodes.The increase is particularly important for mammals (+130%) and to some extant for birds (+73%), while it is minor for other groups of vertebrates.
Despite these figures, it should be noted that cestodes remain known from less than one third of the potential Swiss vertebrate hosts (see Table 2).Metacestodes have been found in 40 invertebrate taxa, an increase from 24 in Fuhrmann (1926), but still an extremely low number that is likely due to the paucity of recent life-cycles studies.
Actinopterygii: There is a long tradition of fish parasitological studies in Switzerland and thus it is logical that the number of host species has only marginally increased since Fuhrmann (from 31 to 36).The tapeworm fauna from most common fishes is generally well known, although the problem of Proteocephalus spp. in whitefish remains unresolved (see above) and will necessitate detailed molecular studies to untangle.Nevertheless, despite the abundant literature and over a century of studies, the helminthes of the smaller or less common species remain poorly explored as tapeworms have been found in only 36% of the fish present in Switzerland (Table 2).An additional difficulty with fish is that introduced or invasive taxa are a problem in some waterbodies.A few of them have acclimated together with their parasite fauna, like the catfish Ameiurus melas (Rafinesque, 1820)

Taxonomic problems
Confidence in cestode identifications reported herein may vary greatly among groups and depends obviously in part on whether recent revisions were made, or failing this, on the quality of initial determination.For many of the cyclophyllidean taxa, no recent taxonomic reassessment was performed, although a number of subgroups have been reviewed (at least in part) in the last two decades including several genera of Hymenolepididae (e.g., Vasileva et al., 1999Vasileva et al., , 2002;;Makarikov & Georgiev, 2020) or of Dilepididae and Paruterinidae (e.g., Georgiev et al., 2004;Komisarovas et al., 2007;Dimitrova et al., 2017).Conversely, Bothriocephallidea and Oncoproteocephalidea have been more extensively reviewed e.g., by Scholz et al. (2007) or Kuchta et al. (2008).It remains that some of the older identifications may need confirmation.Part of the ancient material deposited in museums is, however, now over 100 years old and starting to deteriorate, making their study difficult.The development of molecular tools will certainly also bring new information on the composition and diversity of some taxonomically difficult groups, as recently exemplified by Brabec et al. (2023) but their use for identifying new taxa remain elusive for the time being as a comparative database is lacking.

Comparison with other European faunas
With 251 tapeworm species, the Swiss fauna is proportionally richer than that of other European countries, some of them much larger and with a marine fauna, like Finland (170 spp.), Iberian Peninsula (257 spp.), Slovakia (225 spp.),Poland (279 spp.) (Haukisalmi, 2015) or Italy (323 spp.) (Stoch, 2003).This observation stands even when considering only vertebrate hosts, as some of the above-mentioned reports did not consider invertebrates and metacestodes.For non-landlocked countries, the marine component of the speci fic diversity is obviously significant (e.g., Cyclophyllidea only count for 63% of the Italian specific diversity), but even lacking it, the Swiss fauna is remarkably diverse (61 spp./10'000 sq.km in Switzerland vs. 10.7 in Italy or 8.6 in Poland).By this metrics, Slovakia has the closest diversity (45.9) to Switzerland.Both countries share a landlocked situation at similar latitude, a mountainous landscape, as well as a strong helminthological tradition and therefore a higher number of species examined than in other countries.This last factor is likely the most significant, as also noted by Haukisalmi (2015).
More detailed comparisons of parasites faunas are hazardous as each country has a typical host diversity.However, Haukisalmi (2015, table 1, P6) provided a comparison of unique cestode species numbers per order of birds in various European countries to which we can compare figures for Switzerland.The latter are very similar to those in almost all countries considered, with the highest number of cestodes in Anseriformes, Passeriformes, Gruiformes, Galliformes and Podicepidiformes.

CONCLUSION
Despite lacking a marine fauna, Switzerland hosts a very rich cestode diversity that has been quite extensively studied, especially in the first half of the 20th century.
Since the seminal synthesis of Fuhrmann (1926), our knowledge of tapeworms' diversity in the country expanded significantly, most notably in mammals.This positive trend should, however, be put in perspective, as most of this progress was due to a very limited and quickly waning number of scientists.Presently, not only reports of new taxa are excessively rare and have all but stopped, but regular reports of known species in the wild fauna also became scarce.Among the factors leading to this situation, the vanishing training of taxonomists in this (and many other) group is certainly crucial.Furthermore, the taxonomy of animals like cestodes cannot rely on a population of amateur scientists to complement institutional research and the implementation of alternative (molecular?) systems of identification remain hypothetical at best given the poor comparative database available yet.This is worrying in a context of the threat to global biodiversity, and unfortunate because local taxonomic research would not require heavy investment.
As demonstrated many times, including in Switzerland (e.g., Gigon & Beuret, 1991), a parasitological assessment of even the most common hosts would easily enrich the Swiss fauna and discover new indigenous taxa.This type of survey is, however, unlikely to flourish in the future as administrative agreements for collecting hosts, especially birds and some mammals, become increasingly arduous to obtain (Mariaux, 2021).As a result, today, and despite the number of prominent cestodologists who worked in Switzerland, less than one third of vertebrates in the country are known to harbor cestodes.The true extent of this parasitic fauna hence remains to be described./1914, 1960, 1964, 1968, 1976 Leuciscidae Alburnus alburnus°  Vaucher & Hunkeler 1967, Wahl 1967CH/1931,1964-1974, 1984, 1994, 1996