Three new species and new records of the genus Centromerus (Araneae, Linyphiidae) from Italy

Three new species of the genus Centromerus from Italy, C. tongiorgii sp. nov., C. hanseni sp. nov., and C. gatoi sp. nov., are described for the fi rst time on the basis of both male and female specimens. Their relationships with other congeneric species, as well as their diagnoses, are discussed using morphological characters. New records of poorly known species of Centromerus from Italy are furthermore reported. Among them, C. desmeti Bosmans, 1986 is reported for the fi rst time for the Italian fauna and for continental Europe.

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R e s e a r c h a r t i c l e
urn:lsid:zoobank.org:pub:A920AF4E-6A95-4109-A403-6A93BD444222

Material and methods
Specimens were collected, using pitfall traps or sieving through leaf litter, and fi xed in 75% ethanol for morphological studies. Photographs and measurements were taken at the Systematic Zoology Laboratory, Tokyo Metropolitan University, Japan, using a Canon EOS 60D digital camera mounted on a Nikon SMZ 1270 stereo microscope. Epigynes and vulvae of small specimens were photographed using the same camera mounted on a Nikon Optiphot 2 microscope. Final images were merged using Helicon Focus 6 image stacking software. The left palps of males are illustrated. To study internal structures of female genitalia, epigynes were removed and boiled for 5-6 minutes in a 20% KOH solution. Leg measurements are reported as follows: femur, patella, tibia, metatarsus, tarsus (total length). All measurements are in millimeters. The specimens examined in this study are stored in the Museo Civico di Scienze Naturali "E. Caffi " of Bergamo (   PROSOMA. Carapace uniformly yellowish-brown; chelicerae, labium and gnathocoxae of the same colour. Chelicera with stridulatory ridges on the lateral margin. Three teeth at the anterior margin of the fang groove, posterior margin with 4-5 small denticles. Sternum greyish. Paler, yellowish coloration in some specimens. ABDOMEN. Covered with sparse setae, uniformly greyish with lighter marks barely visible on the dorsal side, distal end with a lighter area. PALP (Figs 1A-D, 2A-C). Patella and tibia bearing 1 robust spine each, tibia with 3 trichobothria. Cymbium with a massive, triangular dorsal hump facing backward followed by a large and stumpy median tubercle. Paracymbium large, bearing several short setae on the basal area, lateral margin covered with several minute wrinkles. Two proximal radical apophyses: radical apophysis I short, robust and spine-like; radical apophysis II long, thin and thread-like, curved outward and downward. Distal radical apophysis bearing one or several robust teeth. Distal suprategular apophysis robust and curved, with a second branch more or less strongly developed depending on the population and individual. Antero-proximal part of median membrane with a row of 8-10 stumpy teeth. Terminal apophysis clearly visible, ending with a wide, wrinkled tip. Embolus curved, ending in a sharp point.  (2020) EPIGYNE AND VULVA (Figs 1E-G, 2D-E). Anterior wall triangular, strongly wrinkled, covering a large epigynal cavity, ending with a truncated tip and lacking a clear ending lobe. Distal part of scapus wide, lobate, strongly protruding from the epigynal cavity. Posterior median plate small and rectangular, longer than wide. Spermathecae elongated and S-shaped. Copulatory grooves fi rst turning posteriorly and outward before returning to the middle part of the vulva and ending in copulatory openings in the distal part of the scapus.

Distribution
Endemic to Italy. Distributed along the Alpine and Apennine mountain ranges, from the Lessini Mountain Prealps to the Aspromonte massif, see Fig. 10.

Diagnosis
Males of the new species generally resemble male Centromerus tongiorgii sp. nov., C. semiater and C. sellarius. They can easily be separated from males of the other three species by the presence of a welldeveloped radical apophysis I (RA-I) which is clearly visible when the palp is observed prolaterally or retrolaterally, in contrast to the absent or non-visible RA-I in males of the other three species. A further diagnostic character is the square, stocky dorsal hump (DT) of male C. hanseni sp. nov., which appears triangular and ending with a sharp or rounded tip in the other three species. In addition, male C. hanseni sp. nov. can easily be separated from male C. tongiorgii sp. nov. and C. semiater by the presence of a well-developed apophysis in the distal part of the paracymbium (APC), clearly visible when the palp is observed ventrally (Fig. 4C), absent in the other two species.

Etymology
The specifi c name is a patronym in honor of Harald Hansen, an Italian arachnologist from Venice who recently passed away (Uliana 2018). Hansen widely contributed to the study of the Italian spider fauna, in particular the family Salticidae. PALP (Figs 3A-D, 4A-C). Patella and tibia bearing one robust spine each, tibia with 3 trichobothria. Cymbium with a stocky, squared dorsal hump. Paracymbium large, with a robust, pointed apophysis headed outward on the distal part, lateral margin covered with several minute wrinkles. Two proximal radical apophyses, one robust, spine-like, the other long, thin and thread-like, both curved outward and  (2020) downward. Distal radical apophysis with several minute denticles. Distal suprategular apophysis robust and curved outward, second branch shorter. Antero-proximal part of median membrane with a row of 9-10 small, stumpy teeth. Terminal apophysis transparent and scarcely visible, ending with a wide, fl at and wrinkled tip. Embolus curved, ending in a sharp point.

Description
The available specimens were in a poor condition of preservation; thus, the colouration of the species might be slightly different in life.
PROSOMA. Carapace uniformly yellowish-brown, chelicerae, labium and gnathocoxae of the same colour. Chelicera with stridulatory ridges on the lateral margin. Three teeth at the anterior margin of the fang groove, posterior margin with 4-5 small denticles. Sternum greyish.
ABDOMEN. Covered with sparse setae, uniformly greyish with lighter marks barely visible on the dorsal side, distal end with a lighter area.

Female
HABITUS. See Fig. 5I (Figs 5E-G, 6D-G). Anterior wall wide, with a round border and two elongated lateral lobes. Basal part of scapus long and strongly protruding ventrally. Distal part of scapus wide and curved. Posterior median plate wide, rectangular, longer than wide. Spermathecae elongated and S-shaped. Copulatory grooves fi rst turning posteriorly and outward before returning to the middle part of the vulva and ending in copulatory openings at the distal part of the scapus. Centromerus cf. paradoxus (Simon, 1884) Figs 7A-B, 8, 10 For a complete list of references, see WSC (2020).

Distribution
Western Mediterranean. In Italy widespread along the entire Apennine mountain chain. See Fig. 10.

Remarks
Records of C. paradoxus have long been considered doubtful for the Italian fauna since Brignoli (1972), thus being omitted in the recent Catalog of the Italian Spiders by Pantini & Isaia (2019). New  (2020) records from Italy herein reported confi rm the presence of a member of the paradoxus species group in the Italian peninsula. The paradoxus species group currently covers a wide distributional area across Europe, with species recorded in the Western Mediterranean (C. paradoxus (Simon, 1884)), Balearic Islands (C. ponsi Lissner, 2016), Carpathian Mountains (C. gentilis Dumitrescu & Georgescu, 1980) and the Balkans (C. acutidentatus Deltshev, 2002 andC. obenbergeri Kratochvil &Miller, 1938) (Nentwig et al. 2020). However, among such species, only minor differences in the diagnostic characters of palp and epigyne can be observed, making their morphological separation tricky. Such interspecifi c similarities suggest the presence of cryptic species or potential misidentifi cation of one or a few species with a wide distribution and high local intraspecifi c variability. In light of these facts, a general revision of this species group, possibly including both morphological and molecular analysis, seems necessary to confi rm the validity of the current taxonomy.
Our specimens from Italy show few morphological differences with congeners such as C. paradoxus and C. acutidentatus, making a specifi c diagnosis diffi cult. In our opinion, the differences observed are insuffi cient to establish a new species. In order to avoid further problems in the already confusing taxonomy of this group, we temporarily attribute the Italian specimens to C. cf. paradoxus, the species which, geographically, is most likely to be present in Italy. Further studies, involving a precise morphological and molecular comparison of all the species of this group, will allow a better identifi cation of the Italian samples.

Remarks
Species widely distributed, but Italian records are sparse and restricted to the north and the south of the country. Our new records confi rm the presence of C. serratus in numerous regions of Central Italy. Bosmans, 1986 Figs 7C-D, 9-10 Centromerus desmeti Bosmans, 1986: 90, fi gs 8-16.

Remarks
This species shows a North African distribution (Bosmans 1986); previously the only European record was from the island of Majorca (Nentwig et al. 2020). New data reported here are the fi rst record of this species for Italy and for Continental Europe.

Discussion
Among the Italian linyphiid fauna, the genus Centromerus appears to be well diversifi ed and speciesrich. Our study increases the number of species recorded from Italy to 30, nine of which are considered endemic to a few localities in Sardinia or the Italian peninsula. The taxonomy and biogeography of species of Centromerus in Italy has long been neglected by modern arachnologists; most of the local species were studied and described by Brignoli in the 1970s (Pantini & Isaia 2019). Only in the last few years has this genus been revised, with the recent discovery of new species (Bosmans & Colombo 2015;Bosmans & Gasparo 2015). The new records reported herein and the description of a further three new species (and a potential fourth), suggest that our knowledge regarding the Italian fauna of Centromerus, and the family Linyphiidae in general, is defi cient. Such a lack of information not only involves the traditionally poorly-explored Italian southern regions or main islands, but also the much better-studied northern area, as highlighted by our discovery of C. tongiorgii sp. nov., a widespread species. Further collection and study regarding the Italian linyphiid fauna is likely to lead to the discovery of several new species.