General taxonomic coverage description: The key includes a total 179 species (supplementary file 1), following the taxonomy and nomenclature recently proposed by Bonato and Minelli (2014).

Applicability and identification units: The key is intended to allow species-level identification of adult or subadult specimens, i.e. specimens with visible gonopods. The key allows also distinguishing the sex. Within a single species, the male and female phenotypes are treated operationally as distinct identification units, because some of the characters employed (different in different species) are also sexually dimorphic, and because some characters are applicable and effective in distinguishing species only for the male but not for the female or vice versa.

Morphological terminology: The key follows the conventional morphological terminology defined and illustrated by Bonato et al. (2010). Relevant body parts are labelled accordingly in the photos illustrating the character states (see below).

Operational methods: Only a few characters can be evaluated properly by means of a stereomicroscope, with incident light and at low magnification. In most cases, it is recommended to examine the specimen by means of a microscope, in transmitted light and at higher magnification, after including the specimen in a non-permanent microscopic slide.

The effective evaluation of some characters requires one or both of the following operations:

– detaching head from trunk. Recommended protocol: keeping the specimen under a stereomicroscope, on soft ground, with the dorsal side upwards; piercing the dorsal membrane between head and forcipular tergite repeatedly by means of a scalpel-like pin;

– detaching the maxillary complex from the remaining part of the head. Recommended protocol: after detaching head from trunk, keeping the head under a stereomicroscope, on a soft ground, with the ventral side upwards; piercing the lateral membranes connecting the second maxillary coxosternite to the pleurites repeatedly by means of a scalpel-like pin.

Further practical instructions are given by Pereira (2000) and Foddai et al. (2002).

Characters: A total of 89 characters have been considered, including 51 binary characters, 37 multistate characters with 3–5 alternative states each, and a “filtering” character (number of leg-bearing segment), which is allowed to assume any integer value up to 999. Of the characters, 15 are depending on the state of another character, therefore their applicability is constrained. The characters have been selected giving priority to those with null or negligible intraspecific variation with respect to our state definitions, and to those that do not require dissection. Among the characters proposed and employed in the literature as diagnostic between species, we excluded those that have been found or suspected to be actually poorly effective, because of either intraspecific variability or artifactual origin (Bonato and Minelli 2014). In the key, characters are arranged in four sections according to the operations required or recommended for their evaluation (Fig. 2): (i) characters that can be evaluated on the entire body, keeping the specimen with the ventral side upwards (“without dissection, ventral view”; 54 characters); (ii) as before, but with the dorsal side upwards (“without dissection, dorsal view”; 13 characters); (iii) characters that can only be evaluated after detaching the head from the trunk, keeping both pieces with the ventral side upwards (“after detaching head from trunk, ventral view”; 12 characters); (iv) characters that can only be evaluated after removing the maxillary complex from the head and keeping both the maxillary complex and the remaining part of the head with their ventral side upwards (“after detaching maxillary complex from head, ventral view”; 9 characters). Within a section, characters are arranged in anatomical order, anterior to posterior, proximal to distal. Characters that are diagnostic at the genus level are highlighted. Most character states are illustrated by microscopic photos taken on specimens of representative species.

Sources of data: Characters have been coded for each species referring to selected published descriptions and illustrations (indicated in the species-file under “Main references”, see below; full references in supplementary file 2). Published information has been ignored when suspected or found to be inaccurate or based on misidentified specimens. For 67 species, data have been confirmed by us or integrated by direct examination of representative specimens, in the Bonato-Minelli collection, at the Department of Biology, University of Padova (supplementary file 1).

For a single species, more than one state have been assigned to a character whenever (i) there is interindividual variation, including sexual dimorphism, or (ii) the actual condition of the character is uncertain in the species, or (iii) subjectivity in evaluation could bring different users to score different states as present in the specimens at hand.

As to the number of leg-bearing segments, almost all species reported from Europe are known or expected to have interindividual variation in the number, the range of variation differing in different species, and the width of variation correlating approximately with the average value (Minelli et al. 2010). For a single species, when the number has been counted in more than a hundred specimens from at least two dozens of localities, the exact range between the recorded minimum and maximum has been adopted as a confident estimate of the intraspecific range of variation. Conversely, when the number has been counted in fewer specimens, and thus the variation in the species is probably underestimated, the intraspecific range has been estimated tentatively by considering the known average figure in the species and hypothesizing a 30% coefficient of variation (which is the average variation estimated in the intensely sampled species, as listed in supplementary file 1). This should not be taken as meaning that all segment numbers between the lowest and the highest value attributed to a given species have been actually recorded, or even occur in nature; discontinuities in the distribution of segment numbers within a species are well known, especially in species with very high segment number (e.g., Minelli and Bortoletto 1988).

Species-files: For any species, the following information is provided in a standardized way: “Valid name” of the species; “Family”; “Other names” (other names frequently used for the species after 1950, including synonyms, different generic combinations and alternative spellings); “Short description”; “Similar species” (selected species that could be misidentified, with main differential characters listed in parentheses); “Distribution” (known distribution in Europe, listing the main geographical areas from where the species has been reported reliably); “Taxonomic notes”; “Main references” (published sources that we considered for the morphology of the species; full citations in supplementary file 2).

Figure 2. 

Screenshot of ChiloKey.

a) http://www.biologia.unipd.it/chilokey/

b) http://www.interactive-keys.eu/chilokey/

Repository: Department of Biology, University of Padova, Padova, Italy

Metadata language: English

Date of metadata creation: 2014-06-05

Platform: Windows Server 2003 - Microsoft Framework. NET 4

Programming Language: Asp.NET

Data base: MS Windows SQLSERVER, IIS6, NET 4.0

Application version: ChiloKey 1.0

Update police: The application can be augmented/updated only by, or in agreement with, the corresponding authors of this paper. Authors keep updated both the web application, by implementing new functions, and the data matrix, by improving encoded descriptions of terminal taxa. Every change can be monitored on the homepage and reported in the TXT export data file, by updating the number of the application version and by changing the date of the last modification to the data matrix. A short message on the homepage may describe differences from the previous version, if needed.

Use of the primary data: Primary data are available from the corresponding authors by agreement.

Licence for the use of the key: Creative Commons Attribution License 3.0 (CC-BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.