Fauna Europaea: Gastrotricha

Abstract Fauna Europaea provides a public web-service with an index of scientific names (including important synonyms) of all living European land and freshwater animals, their geographical distribution at country level (up to the Urals, excluding the Caucasus region), and some additional information. The Fauna Europaea project covers about 230,000 taxonomic names, including 130,000 accepted species and 14,000 accepted subspecies, which is much more than the originally projected number of 100,000 species. This represents a huge effort by more than 400 contributing specialists throughout Europe and is a unique (standard) reference suitable for many users in science, government, industry, nature conservation and education. Gastrotricha are a meiobenthic phylum composed of 813 species known so far (2 orders, 17 families) of free-living microinvertebrates commonly present and actively moving on and into sediments of aquatic ecosystems, 339 of which live in fresh and brackish waters. The Fauna Europaea database includes 214 species of Chaetonotida (4 families) plus a single species of Macrodasyida incertae sedis. This paper deals with the 224 European freshwater species known so far, 9 of which, all of Chaetonotida, have been described subsequently and will be included in the next database version. Basic information on their biology and ecology are summarized, and a list of selected, main references is given. As a general conclusion the gastrotrich fauna from Europe is the best known compared with that of other continents, but shows some important gaps of knowledge in Eastern and Southern regions.


Introduction
The European Commission published the European Community Biodiversity Strategy, providing a framework for development of Community policies and instruments in order to comply with the Convention on Biological Diversity. This Strategy recognises the current incomplete state of knowledge at all levels concerning biodiversity, which is a constraint on the successful implementation of the Convention. Fauna Europaea contributes to this Strategy by supporting one of the main themes: to identify and catalogue the components of European biodiversity into a database in order to serve as a basic tool for science and conservation policies.
With regard to biodiversity in Europe, both science and policies depend on a knowledge of its components. The assessment of biodiversity, monitoring changes, sustainable exploitation of biodiversity, and much legislative work depend upon a validated overview of taxonomic biodiversity. Towards this end Fauna Europaea plays a major role, providing a web-based information infrastructure with an index of scientific names (including important synonyms) of all living European land and freshwater animals, their geographical distribution at country level and some additional useful information. In this sense, the Fauna Europaea database provides a unique reference for many user-groups such as scientists, governments, industries, conservation communities and educational programs.
Fauna Europaea started in 2000 as an EC-FP5 four-years project, delivering its first release in 2004(Jong et al. 2014. After thirteen years of steady progress, in order to efficiently disseminate the Fauna Europaea results and to increase the acknowledgement of the Fauna Europaea contributors, novel e-Publishing tools have been applied to prepare data-papers of all major taxonomic groups. For this purpose a special Biodiversity Data Journal Series has been compiled, called Contributions on Fauna Europaea. This work was initiated during the ViBRANT project and is further supported by the recently started E U BON project. This paper holds the first publication of the Fauna Europaea Gastrotricha data sector as a BDJ data paper.
Within the EU BON project also further steps will be made to implement Fauna Europaea as a basic tool and standard reference for biodiversity research and to evaluate taxonomic expertise capacity in Europe. The Fauna Europaea data-papers will contribute to a quality assessement on biodiversity data by providing estimates on gaps in taxonomic information and knowledge.

General description
Purpose: The Fauna Europaea is a database of the scientific names and distribution of all living, currently known European land and fresh-water animal species assembled by a large network of experts, using advanced electronic tools for data collations and validation routines. An extended description of the Fauna Europaea project can be found in Jong et al. 2014). A summary is given in the sections below.
The Gastrotricha are one of the 58 Fauna Europaea major taxonomic groups, and currently number 326 freshwater species worldwide, 224 of which reported from Europe. The data were acquired and checked by 5 specialists. No division of the taxa groups to be checked has been set among the specialists, thus all the specialists have to be considered responsible for the available data ( Fig. 1

Addititional information: Gastrotricha
The phylum Gastrotricha currently (May 2015) counts 813 species of free-living, microinvertebrates commonly present and actively moving on and into the sediments of aquatic ecosystems where they represent a significant component of meiofauna, with densities up to 364 ind/cm in marine sands and 168 ind/cm in freshwater sediments (Nesteruk 1993, Nesteruk 1996, Todaro and Hummon 2008. FaEu data set Gastrotricha species per family: the updated number of species is reported in brackets. See Table 1 for family statistics. Gastrotricha have 'Aschelminthes' or 'pseudocoelomates' features such as a worm-like body, a complete intestine, and a primary body cavity even if almost vestigial (Hyman 1951). Morphological and ultrastructural studies support a sister-group relationship of Gastrotricha with Cycloneuralia or with Ecdysozoa, whereas molecular analyses mainly carried out on the gene 18S rDNA have suggest to include the phylum into the Platyzoa, close to Gnathostomulida and acoelomate forms (for an overview of the major phylogenetic scenarios concerning Gastrotricha among the Bilateria as well as the internal relationships of the phylum, see Kieneke andSchmidt-Rhaesa 2015). Recent studies based on a trascriptomic-phylogenomic approach found the gastrotrichs to be the sister taxon of the Platyhelminthes (e.g. Egger et al. 2015).
Classical morphological taxonomy recognizes two orders, Macrodasyida and Chaetonotida, quite different in general morphology, biology and ecology (Balsamo and Todaro 2002, Kieneke and Schmidt-Rhaesa 2015.
The order Macrodasyida includes 356 species (10 families, 35 genera), all interstitial, marine or brackish-water except for only 2 freshwater species. The marine monotypic genus Hemidasys has been considered extinct by Hummon and Todaro (2010). The vast majority of Chaetonotida, 335 species, colonize fresh waters, with a clear preference for eutrophic habitats, where most species known so far live as epiphytic or periphytic. Only about 70 freshwater species have been found in psammic habitats, and less than 35 species are known from sediments of running waters. Two entire families (Dasydytidae and Neogosseidae), with about 50 species, are semipelagic or fully planktonic: the colonization of water column corresponds to specific, characteristic morphological adaptations (Kisielewski 1981, Kisielewski 1990, Schwank 1990, Ricci and Balsamo 2000, Kånneby and Todaro 2015. Gastrotrichs share several morphological and physiological features with other groups of freshwater microinvertebrates: among them are small size, soft body, worm-like body shape, high contractility, adhesive glands, ciliary locomotion, triradiate pharynx with welldeveloped musculature, short life cycle, common parthenogenic reproduction, production of resting stages (d'Hondt 1971). But the adaptive potential of freshwater Gastrotricha is relatively limited compared to other animal phyla like Rotifera or Nematoda, so that their distribution appears to be narrower and to current knowledge it does not extend to extreme habitats.
The diversity of the phylum Gastrotricha is not very high, but these animals, as a part of the microphagous benthic community, play a significant ecological role in aquatic environments, linking the microbial loop to the higher trophic levels .

Taxonomy and taxonomical issues
The order Macrodasyida includes only 2 freshwater species: Redudasys fornerise, belonging to the family Redudasyidae (which also comprises a marine species, see , and Marinellina flagellata, which was previously assigned either to Macrodasyida (Ruttner-Kolisko 1955, Kisielewski 1987 or to Chaetonotida, in the freshwater family Dichaeturidae (Remane 1961) and is now considered a Macrodasyida incertae sedis. It is the only Macrodasyida species known from Europe, where it was found only once in Austria (Ruttner-Kolisko 1955).
Thanks to recent studies, the current systematics is relatively stable for the order Macrodasyida (Todaro et al. 2006, Hummon and Todaro 2010, Todaro et al. 2011, except for the monotypic genus Marinellina (still incertae sedis). By contrast, the taxonomy of the order Chaetonotida has been repeatedly revised in the last decades and is still unstable especially at the species level (Schwank 1990, Kisielewski 1991, Kisielewski 1997, Kisielewski 1998, Leasi and Todaro 2008, Hummon and Todaro 2010). Furthermore, a phylogenetic study based on molecular markers found the largest chaetonotidan family, Chaetonotidae, and most of the genera included in it to be nonmonophyletic (Kånneby et al. 2013).
Actually, the taxonomy of the phylum has been founded on morphological traits both of the external structure and the internal anatomy, like the shape and size of the cuticular elements, the organization of the reproductive system and the fine structure of spermatozoa (Marotta et al. 2005, Hummon and Todaro 2010). However, especially in Chaetonotida, several of these taxonomical characters appear to vary, even considerably, at species level and in some cases also at genus level, which makes taxonomic identification quite problematic (Schwank 1990).
It must be said that Gastrotricha, small and diaphanous, should be observed alive with a very good microscopical equipment in order to recognize and measure all the morphological details taxonomically important ). That is not always possible, considering the technical problems of collecting samples, maintaining them in the lab, searching for in them in the sediments under a stereomicroscope, and then isolating single specimens be anesthetized in some manner and to allow proper observation. However, several freshwater species can be suitably fixed and observed later with good results (Giere 2009).
The recent introduction of molecular analyses to Gastrotricha has opened new perspectives in the study of phylogenetical relationships; an integrative taxonomical approach using both morphological and molecular methods seems essential to effectively revise the current classification according to phylogenetic relationships , Paps and Riutort 2012, Kånneby et al. 2013.
We may expect a future increase in species numbers of Chaetonotidae and possibly of Dasydytidae. A reliable assessment of the estimated species number cannot be advanced due to the sporadic nature of faunistic findings and samplings, but a reasonable minimal estimate of possible increase in number of species known is advanced based on the current knowledge of unpublished data (Table 1).

European freshwater species
The Fauna Europaea database (version 2.4, January 2011) includes 215 species, 214 of which belong to the order Chaetonotida (4 families) and a single species incertae sedis is a member of the order Macrodasyida.
Eight additional species of Chaetonotida have been described and another one has been recorded first for Europe after the release of the database, so that currently European freshwater species of Gastrotricha known so far add up to 224 overall (223 Chaetonotida + 1 Macrodasyida), that are considered in the present paper.
A synthesis of European taxa is presented below.

Family Chaetonotidae (Fig. 2 A-F)
Tenpin-like body, 84-770 µm in length.Two adhesive tubes forming the caudal 'furca'. Four cephalic ciliary tufts. Cuticle generally provided with ornamentations of various shape and size, in some cases smooth. Two longitudinal ventral ciliary locomotory bands. Pharynx  This family is the largest one of the order, and includes most of the epibenthic and periphytic species colonizing standing waters as well as the few interstitial species known from psammic habitats.
At global scale the family Chaetonotidae includes 277 freshwater species (10 genera).
All species of Dasydytidae are freshwater, semiplanktonic and planktonic in standing waters.
At global scale the family Dasydytidae includes 42 species in 7 genera.

Family Dichaeturidae
Cylindrical body, 98-150 µm in length. Two pairs of adhesive tubes forming the caudal furca. Cephalic ciliature uniform and continuous with 2 ventral ciliary locomotory bands. Cuticle smooth. A dorsal, transverse series of some thin, straight bristles or spines anterior to the furca. Pharynx cylindrical. Sexuality unknown.
All species of family Dichaeturidae are freshwater, very rare, semiplanktonic in standing waters.
At global scale the family Dichaeturidae includes 4 species of a single genus.
In European fresh waters the family Dichaeturidae is represented by 3 species in the single genus Dichaetura.
Family Neogosseidae (Fig. 2 G) Tenpin-like body, 90-310 µm in length (caudal spines excluded). Caudal furca absent: trunk end rounded or truncated with 2 short, caudal protuberances and 2 pairs or an unpaired median group of long simple or barbed spines. One dorsal and 2 ventral cephalic interrupted transverse ciliary bands. Cuticle smooth or with numerous fine spined scales. Several pairs of ventral ciliary locomotory tufts or oblique bands. Thick pharynx with 1-4 bulbs. Parthenogenic.
All the species of family Neogosseidae are freshwater, semiplanktonic or planktonic in standing waters.
At global scale the family Neogosseidae is composed of 9 species in 2 genera.
In European fresh waters the family is represented by 4 species in 2 genera: Neogossea (3) and Kijanebalola (1 species, finding doubtful).
Family Proichthydiidae, the only other family of Chaetonotida exclusively freshwater, includes 2 species of 2 monotypic genera (Proichthydium, Proichthydioides): it is known from Brazil and Japan but has not yet been reported from Europe.
This single species of the genus was found only once from Austrian interstitial fresh waters.

Project description
Title: This BDJ data paper includes the taxonomic indexing efforts in the Fauna Europaea on European Gastrotricha covering the first two versions of Fauna Europaea worked on between 2000 and 2013 (up to version 2.6).

Personnel:
The taxonomic framework of Fauna Europaea includes partner institutes, providing taxonomic expertise and information, and expert networks taking care about data collation.
Every taxonomic group is covered by at least one Group Coordinator responsible for the supervision and integrated input of taxonomic and distributional data of a particular group. The Fauna Europaea checklist would not have reached its current level of completion without the input from several groups of specialists. The formal responsibility of collating and delivering the data of relevant families rested with a number of Taxonomic Specialists (see Table 1).

For Gastrotricha the responsible Group Coordinator and Taxonomic specialist is Maria
Balsamo, who is also Taxonomic Specialist, together with the other Associated Specialists listed in Table 2. A more detail overview of the Fauna Europaea classification and expertise network for Gastrotricha can be found here: http://www.faunaeur.org/ experts.php?id=21.  On the available expert capacity, presently, in Europe faunistic, systematic and taxonomical studies on freshwater Gastrotricha species are actively carried out in Italy (Uni versity of Urbino), in France (MNHN) and in Sweden (NRM) by around five specialists. Some additional ultrastructural and phylogenetical work is done on Gastrotricha in Germany (Senckenberg & University of Hamburg). Outside Europe around six more specialists contribute to the taxonomy of (marine and freshwater) Gastrotricha.

Study area description:
The area study covers the European mainland (Western Palearctic), including the Macaronesian islands, excluding the Caucasus, Turkey, Arabian Peninsula and Northern Africa (see: Geographic coverage).
Design description: Standards. Group coordinators and taxonomic specialists have to deliver the (sub)species names according to strict standards. The names provided by Fauna Europaea are scientific names. The taxonomic scope includes issues like, (1) the definition of criteria used to identify the accepted species-group taxa, (2) the hierarchy (classification scheme) for the accommodation of the all accepted species and (3), relevant synonyms, and (4) the correct nomenclature. The Fauna Europaea 'Guidelines for Group Coordinators and Taxonomic Specialists', include the standards, protocols, scope, and limits that provide the instructions for all more than 400 specialists contributing to the project, strictly following the provisions of the current edition of the International Code of Zoological Nomenclature.
Data management. The data records could either be entered offline into a preformatted MS-Excel worksheet or directly into the Fauna Europaea transaction database using an online browser interface (Fig. 3).

Sampling methods
Study extent: See spatial coverage and geographic coverage descriptions.

Fauna Europaea on-line (browser interfaces) and off-line (spreadsheets) data entry tools.
Sampling description: Fauna Europaea data have been assembled by principal taxonomic experts, based on their individual expertise, including literature sources, collection research, and field observations. In total no less than 476 experts contributed taxonomic and/or faunistic information for Fauna Europaea. The vast majority of the experts are from Europe (including EU non-member states). As a unique feature, Fauna Europaea funds were set aside for rewarding/compensating for the work of taxonomic specialists and group coordinators.
To facilitate data transfer and data import, sophisticated on-line (web interfaces) and offline (spreadsheets) data-entry routines were built, integrated within an underlying central Fauna Europaea transaction database (see Fig. 3) This includes advanced batch data import routines and utilities to display and monitor the data processing within the system. In retrospect, it seems that the off-line submission of data was probably the best for bulk import during the project phase, while the on-line tool was preferred to enter modifications in later versions. This system works well, but will be replaced after 2013.
A first release of the Fauna Europaea index via the web-portal has been presented at 27 of September 2004, the most recent release (version 2.6.2) was launched at 29 August 2013. An overview of Fauna Europaea releases can be found here: http:// www.faunaeur.org/about_fauna_versions.php.
Quality control: Fauna Europaea data are unique in a sense that they are fully expert based. Selecting leading experts for all groups assured the systematic reliability and consistency of the Fauna Europaea data. Furthermore, all Fauna Europaea data sets are intensively reviewed at regional and thematic validation meetings, at review sessions on taxonomic symposia (for some groups), by Fauna Europaea Focal Points (during the FaEu-NAS and PESI projects) and by various end-users sending annotations using the web form at the web-portal. Additional validation on gaps and correct spelling was effected at the validation office in Paris.
In general we expect to get taxonomic data for 99.3% of the known European fauna after the initial release. The faunistic coverage is not quite as good, but is nevertheless 90-95% of the total fauna. For Gastrotricha the current taxonomic coverage is about 96% (see Table 1), and the distribution of faunistic data by country is quite heterogeneous, according to the nationality of researchers.
Checks on technical and logical correctness of the data have been implemented in the data entry tools, including around 50 "Taxonomic Integrity Rules". This validation tool proved to be of huge value for both the experts and project management, and contributed significantly to preparation of a remarkably clean and consistent data set. This thorough reviewing makes Fauna Europaea the most scrutinised data sets in its domain.
The only other existing database specifically dedicated to freshwater species on a worldwide scale has been produced within FADA (Freshwater Animal Diversity Assessment Project), but it has not yet been published. A number of freshwater species th appear also in the WoRMS (World Register of Marine Species) taxonomic database of Gastrotricha, since some species have been occasionally reported from brackish waters.
Step description: By evaluating team structure and life cycle procedures (data-entry, validation, updating, etc.), clear definitions of roles of users and user-groups, according to the taxonomic framework were established, including ownership and read and writes privileges, and their changes during the project life-cycle. In addition, guidelines on common data exchange formats and codes have been issued (see also the 'Guidelines for Experts' document).  Fig. 4).

Geographic coverage
The focus is on species (or subspecies) of European animals of terrestrial and freshwater environments. Species in brackish waters, occupying the marine/freshwater or marine/ terrestrial transition zones, are generally excluded.
The four species of Chaetonotida only known from brackish waters have been included in the database, in which their particular habitat has been specified.

Taxonomic coverage
Description: This data paper covers the Gastrotricha content of Fauna Europaea, including 4 families, 214 species, 5 subspecies and 199 species synonyms of Chaetonotida and one species incertae sedis of Macrodasyida (Fig. 1, Table 1).
Not all the species described to date are included in the current version of the Fauna Europaea database. The next version of the Fauna Europaea database will be updated with the most recent records.
The placement of the genus Marinellina, the only one freshwater European Macrodasyida, is uncertain. In the database it was considered as a member of the family Turbanellidae in the order Macrodasyida Remane, 1925 (Rao andClausen 1970), but since the taxonomic position of this genus is now actively debated, it is here reported as 'incertae sedis' according to the recent literature.