1. Introduction

2. Materials and Methods

3. Results

3.1. Gastrotrichs

Records of Italian freshwater gastrotrichs apparently cover a 239-year time frame. However, initial data come from simple species lists, lacking any morphometric information on the reported taxa. Consequently, these accounts should treated with caution. For instance, Marcolongo [24] believed the first recorded Italian freshwater gastrotrich be the “hairy soft animal” that Bonaventura Corti found in Modena (see Corti, 1774, Tav. II, Figure XI) [19], and that Eherenberg [52] identify with Chaetonotus maximus Eherenberg, 1838. However, the animal depicted by Corti [19] hardly can be identified as a gastrotrich; its elongate body without the trademark caudal furca makes it resembling most to a microturbellarian instead (a copy Corti’s paper can be found at the following url: https://archive.org/details/osservazionimic00corti/page/n209/mode/2up).

Similarly, we could not confirm the finding of Lepidodermella squamata (Dujarden, 1841) near Trieste (Region Friuli Venezia Giulia) attributed to Grüspan, 1908 [37] by Marcolongo [24] and Mola [25]. On the other hand, based on our bibliographic search the following historical records are confirmed: presence of Ichthydium podura (Müller, 1773) and Chaetonotus larus Müller, 1773 in Valcuvia (Lombardia region) Maggi [20]; occurrence of Heterolepidoderma ocellatum Metschnikoff, 1865 in the Euganean thermal waters (Veneto region) Issel [21]), and of Chaetonotus chuni Voigt, 1901 near Pavia (Lombardia region) Zacharias [22].

The first information on the Italian species including morphometric data comes from the taxonomic study by the Italian researcher Ines Marcolongo, who investigated the Astroni crater lake near Naples and reported 17 species, eight of which were described as new to science [23,24]. The most recent published records of Italian freshwater species can be found in two phylogenetic works by Kånneby et al. [32,33], which list Chaetonotus schultzei, Lepidochaetus zelinkai (Grünspan, 1908) and Polymerurus nodicaudus (Voigt, 1901), all found in Lake Pratignano, in the province of Modena [32,33].

Although the period covered by the published literature is relatively broad, the intensity of the studies has remained not constant over time. Relatively long periods of stasis were followed by an energetic and productive investigative activity, although often restricted to single regions (e.g., Manfredi [38] in Lombardia; Mola [25] in Sardinia). It is only since 1977 that the Italian gastrotrichs have become the subject of constant and more extensive studies [26,27,28,29,39], and the last decade of the past century proved particularly fruitful in shedding light on the surprising diversity of gastrotrichs in the Italian inland waters. During that period, a series of investigations carried out by researchers of the University of Modena and Reggio Emilia (Italy) headed by professors Maria Balsamo and Paolo Tongiorgi, significantly contributed to the increase in the number of species and of Italian regions involved in the survey [30,31,42,43,44].

From our analysis, it emerges that the number of freshwater gastrotrich species currently known for the Italian inland waters amounts to 91 (Table 3 and Table S1), all belonging to the order Chaetonotida. The 91 Italian species, distributed in 17 genera and three families, were found by investigating 61 localities/biotopes and 81 sites (i.e., sampling points). However, of the 20 Italian regions, less than half (nine regions) have been investigated to some extent with regard to the freshwater gastrotricofauna (Table 3 and Table S1).

The number of species found in the investigated locations (loc) range between 1 and 33, with an average of 5.33 ± 6.13 spp/loc (Table 4). The location for which the highest number of species has been reported (33 species) is Monte Bondone, in the Trentino Alto Adige region. This figure is reached by pooling data from samples collected from several circular water bodies locally known as Viotte or Viote. These are craters created by the explosion of artillery shells during World War I, which were then filled with rainwater [44].

Currently, 19 species are considered endemic to Italy (i.e., so far recorded only in this country), of which 12 have their distribution limited to only one of the nine investigated regions. Italy counts 17 type localities concerning the freshwater gastrotrich species, some of which are such for more than one species (Table 3). Lepidodermella squamata, found in 27 localities, appears to be the most frequently found species in the Italian inland waters (Table 4).

The distribution of the investigated localities, as well as the richness and diversity of the fauna, appears uneven. The most studied regions are Emilia Romagna, Sardinia and Tuscany, while the others have been little or not at all investigated (Table 4). The most surveyed region by far is Sardinia, with 21 localities investigated and 34 species found (averaging 1.81 ± 0.93 spp/loc). Most information on the rich gastrotrich fauna of Sardinia dates back to more than 90 years and no additional records have been added since the work by Mola [25], with the exception of three species new to Sardinia reported by Fregni et al. [31].

In his seminal work on the Sardinian gastrotrichs, Mola [25] also proposed an interesting new classification for the group, including new subclasses, orders, families, genera etc. However, Mola’s classification was not followed/adopted by succeeding specialists, probably because of the language barrier (the article is written in Italian); of the taxa proposed by Mola [25], only the name Wolterecka figures in the current classification of the Gastrotricha, to designate a subset of the vast genus Chaetonotus [53].

The second region based on localities investigated is Emilia Romagna, with 14 biotopes studied and 28 species collected (averaging 4.57 ± 3.08 spp/loc). Data from this region are among the most recent, the latest of which date back to 2013 [33]. Although Tuscany ranks only third in terms of localities investigated (10 locations), it occupies the first position regarding the number of species found (41 spp). The most recent information from Tuscany dates back about 25 years and comes from surveys conducted in lotic waters in the province of Pisa [31]. Despite the low number of sites surveyed, Campania, Trentino Alto Adige, and Lazio host a relatively high number of species found and occupy the first, second, and third places, respectively, in terms of species abundance (number of species per locality, Table 4). The Campania records dates more than a century ago, and the reported simplified anatomy of some of the described species leaves doubts as to their reliability, also considering the poor optical instrumentation in use at that time [23,24]. In contrast, the information from Trentino Alto Adige and Lazio is relatively recent and derived from methodologies in line with current taxonomic practices (e.g., interferential contrast microscopy [44]).

The diversity of the Italian gastrotrich fauna, understood as the number of species, does not seem to be related to the number of localities investigated as much as to the type of biotope studied; eutrophic environments characterized by rich and varied aquatic vegetation seem to offer the best conditions for the development of a highly diversified biocoenosis [27]. However, the peculiarity of fauna associated with oligohaline environments at high altitudes or with biotopes whose waters are characterized by a low pH value, such as pit moss, and even the interstitial environments should be emphasized [29,31]. Planning future research should take all these considerations into account.

Multivariate statistical analyses based on presence/absence data indicate a higher faunal similarity between Emilia Romagna, Tuscany, Trentino Alto Adige, and Lazio than the other investigated regions (Figure 14 and Figure 15). However, it must be taken into account that these results are greatly affected by the different sampling efforts applied to the different regions and by the different taxonomic techniques that have occurred over the long period between the collection of the first data [23] and the most recent ones [31].

Figure 2. Cluster analysis result showing hierarchical clustering of the investigate regions based on Bray-Curtis similarity index on presence/absence of freshwater gastrotrich species.

Figure 2. Cluster analysis result showing hierarchical clustering of the investigate regions based on Bray-Curtis similarity index on presence/absence of freshwater gastrotrich species.

Figure 3. Result of the nMDS analysis showing the ordination of the investigated regions based on the Bray Curtis similarity index on presence/absence of freshwater gastrotrich species.

Figure 3. Result of the nMDS analysis showing the ordination of the investigated regions based on the Bray Curtis similarity index on presence/absence of freshwater gastrotrich species.

3.2. QGIS and Web Map

The first screen of the interactive map that is offered to the user shows a map containing two panels through which specific searches can be made: i) the panel zoom, through which the user can zoom in and out the areas of interest, and ii) the panel layers, through which the user can query the system in search for the information of interest (Figure 4).

Figure 4. Example of the interactive map dedicated to the Italian freshwater Gastrotricha. Screenshot of the initial view of the web map with indications for interactivity: the panel zoom at the top left, and the panel layers at the top right (sovraimposed is an image showing some of the contained layers). Records appear clustered in six large groups based on reciprocal distance. Numbers at the center of the groups indicate the records associated to each cluster.

Figure 4. Example of the interactive map dedicated to the Italian freshwater Gastrotricha. Screenshot of the initial view of the web map with indications for interactivity: the panel zoom at the top left, and the panel layers at the top right (sovraimposed is an image showing some of the contained layers). Records appear clustered in six large groups based on reciprocal distance. Numbers at the center of the groups indicate the records associated to each cluster.

Regarding interactivity, the most important panel is probably the panel layers (Figure 4). It contains 98 layers in total, one of which represents the reference map (eSRI satellite). All the other layers, except one, can effectively express their contents only if activated in conjunction with the reference map (e.g., Figure 5 and Figure 7). The exception is the layer containing the summary data of each Italian region, which may fully show its information even in the absence of the reference map (see below).

For this research, the comprehensive layer Italy-All-Species assumes particular relevance. Activating this layer, in conjunction with the reference map, allows the visualization of all the vector points within the Italian political boundaries, i.e., it visualizes all the points/locations in which gastrotrich species have been found.

Since it was chosen the points to be shown clustered, the initial screen shows six large clusters, in which the vector points are grouped based on their mutual geographical distance (Figure 4). Progressive zooming moves to increasingly smaller clusters until one can visualize the individual sampling points (Figure 5A–C).

Once the point (location) of interest has been exposed, a number at the disk’s center indicates how many records (i.e., species) are associated with that location. Clicking on the disk makes it possible to “explode” the records, which will be displayed surrounding the point itself (Figure 5D). A click on the single record opens a popup box containing all the salient information about that record, e.g., the individual species name, locality, geographical coordinates, bibliographic reference etc. (Figure 6). In short, the popup box reports the 15 attributes chosen to be visualized to the end user, as they are the most valuable. The remaining 11 attributes (see data matrix above) are visible only to the authors (us) on the QGIS desktop platform to facilitate the housekeeping of the dataset.

Figure 5. Examples of the interactive map dedicated to the Italian freshwater Gastrotricha. Screenshots of the web map with the layers Italy-All-Species and the reference map active. The images show the vectors grouped into more or less comprehensive clusters depending on the scale (zoom), from the smallest scale (A) up to progressively larger scales (B–D). The numbers at the center of the groups indicate the records associated with the individual clusters. At the largest scale, the point (location) of interest is reached/shown, and clicking it will display the associated records surrounding the point itself (D).

Figure 5. Examples of the interactive map dedicated to the Italian freshwater Gastrotricha. Screenshots of the web map with the layers Italy-All-Species and the reference map active. The images show the vectors grouped into more or less comprehensive clusters depending on the scale (zoom), from the smallest scale (A) up to progressively larger scales (B–D). The numbers at the center of the groups indicate the records associated with the individual clusters. At the largest scale, the point (location) of interest is reached/shown, and clicking it will display the associated records surrounding the point itself (D).

If activated, the layer Localities offers the overall glimpse of the distribution of the investigated localities and along the Italian territory (Figure 7). Clicking on the individual vector points activates a popup card with the relevant information of the location, including geographical and bibliographic information (Figure 7).

The layers dedicated to the individual species appear to be highly effective in conveying helpful information; by activating them in conjunction with the reference layer, the web map shows the known distribution on the Italian territory of the species of interest; it is, therefore, possible to immediately understand whether it is widespread or confined to a single water body. Paradigmatic examples are shown in Figure 7, where the distribution of a rare (Figure 8A) and of a relatively common species (Figure 8B) is shown.

Figure 6. Example of the interactive map dedicated to the Italian freshwater Gastrotricha. The same image as Figure 5D, showing the popup box associated with one of the records.

Figure 6. Example of the interactive map dedicated to the Italian freshwater Gastrotricha. The same image as Figure 5D, showing the popup box associated with one of the records.

Figure 7. Example of the interactive map dedicated to the Italian freshwater Gastrotricha. Screenshot of the interactive map originating from the layer Localities, showing the distribution of the investigated locations along the national boundaries.

Figure 7. Example of the interactive map dedicated to the Italian freshwater Gastrotricha. Screenshot of the interactive map originating from the layer Localities, showing the distribution of the investigated locations along the national boundaries.

Figure 8. Examples of the interactive map dedicated to the Italian freshwater Gastrotricha. Maps showing the distribution of individual species. (A) Chaetonotus arethusae, with distribution limited to a single biotope; (B) Chaetonotus aemilianus, with a wide distribution.

Figure 8. Examples of the interactive map dedicated to the Italian freshwater Gastrotricha. Maps showing the distribution of individual species. (A) Chaetonotus arethusae, with distribution limited to a single biotope; (B) Chaetonotus aemilianus, with a wide distribution.

The layer Type Localities is significant because it indicates the locations where one or more species were originally described from, and therefore, these sites could be the focus of conservation projects (Figure 9A). Similarly, the layer Endemic Species is exceptionally informative because it indicates sites where the Italian endemic species have been found, so this layer can also be used to direct possible conservation efforts (Figure 9B).

Figure 9. Examples of the interactive map dedicated to the Italian freshwater Gastrotricha. Screenshots of the map showing the distribution of type localities (A) and type locality of the endemic species (B).

Figure 9. Examples of the interactive map dedicated to the Italian freshwater Gastrotricha. Screenshots of the map showing the distribution of type localities (A) and type locality of the endemic species (B).

The layer Regions-Freshwater is also of great interest because it allows rapid access to summary information on the taxa and the sampling effort regarding the individual Italian regions. The map shows the regional borders and each region can be activated to show a popup box containing information relating to the selected region, including the number of species found, locations investigated, etc. (Figure 9). The interactive map can provide all the valuable information quickly and effectively, like (and probably more than) a detailed scientific article.

Figure 8. Layer Regions-Freshwater, by clicking on one of the investigated regions (in the example the Emilia Romagna region), a pop-up box appears with the summary data relating to the investigated locations and the species found, as well as the most common species at regional level and its image.

Figure 8. Layer Regions-Freshwater, by clicking on one of the investigated regions (in the example the Emilia Romagna region), a pop-up box appears with the summary data relating to the investigated locations and the species found, as well as the most common species at regional level and its image.

4. Conclusions

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