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26 August 2022 Thanatus aridorum Šilhavý, 1940 from Czechia is a junior synonym of Thanatus formicinus (Clerck, 1757) (Araneae: Philodromidae)
Milan Řezáč, Vlastimil Růžička
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We revised the type material of Thanatus aridorum Šilhavý, 1940, and noticed that it is a subadult female. Consideration of morphological characters of the three Thanatus species which co-occur at the type locality of T. aridorum led us to conclude that it is a junior synonym of Thanatus formicinus (Clerck, 1757), new synonymy.

Das Typenmaterial von Thanatus aridorum Šilhavý, 1940 wurde untersucht und dabei festgestellt, dass es sich um ein subadultes Weibchen handelt. Die Betrachtung der morphologischen Merkmale der drei an der Typuslokalität von T. aridorum vorkommenden Arten der Gattung Thanatus führten zu dem Ergebnis, dass es sich um ein jüngeres Synonym von Thanatus formicinus (Clerck, 1757), neues Synonym, handelt.

Zrevidováním typového exempláře druhu Thanatus aridorum Šilhavý, 1940 jsme zjistili, že se jedná o nedospělou samici. Porovnali jsme jí se subadultními samicemi všech tří druhů rodu Thanatus vyskytujících se na Mohelenské hadcové stepi a na základě velikosti a tvaru pre-epigyny jsme došli k závěru, že se jedná o nedospělou samici druhu Thanatus formicinus (Clerck, 1757), nová synonymie.

The serpentinite steppe near Mohelno in South Moravia (today Mohelenská hadcová step National Nature Reserve) was very popular among Czech zoologists during the second world war as it was the only steppe with a rich Pannonian fauna that remained in Czech territory at that time. František Miller (1902–1983) performed very detailed faunistic and taxonomic research on spiders at this site (Miller 1943, 1947, 1949). Type material of five valid spider species comes from this site (Růžička et al. 2005) – syntypes of Erigonoplus jarmilae (Miller, 1943), Civizelotes pygmaeus (Miller, 1943) and Altella biuncata (Miller, 1949), as well as paratypes of Zelotes aurantiacus Miller, 1967 and Theonina kratochvili Miller & Weiss, 1979. More recently, spiders at this site were studied by Jan Buchar (Buchar 1997).

Harvestmen from this site were studied by another prominent Czech arachnologist, Vladimír Šilhavý (1913–1984) (Šilhavý 1948). Šilhavý was also involved in spider research at this site. He described two Thanatus (Araneae: Philodromidae) species from there (Šilhavý 1940, 1941). The second one, Thanathus dvoraki Šilhavý, 1941, was synonymised with Thanatus arenarius by Miller (1971), but the first one, Thanatus aridorum Šilhavý, 1940, is still listed as a valid species (cf. World Spider Catalog 2022, Nentwig et al. 2022). In this short contribution, we demonstrate that the first Šilhavý species is a junior synonym of Thanatus formicinus (Clerck, 1757).

Material and methods

In order to check the identity of Thanatus aridorum, we searched for the single type specimen mentioned in the original description (Šilhavý 1940). According to Růžička et al. (2005), it was deposited at the National Museum, Prague (NMPC). We found it there under the inventory number P6E-2870. The original label (Fig. 1f) states Mohelno as the site, 1937 as the collecting year and V. Šilhavý as the collector. The specimen in the vial (Fig. 1d) is without an epigyne (Fig. 1e), the epigyne is conserved separately on a permanent microscopic slide (Fig. 1f). The type specimen was photographed with a Hirox Japan digital microscope and its epigyne was photographed with a Nikon Eclypse 80i.

We compared this specimen with the three Thanatus species known to occur at the type locality of Thanatus aridorum (Kůrka 1997, Buchar & Růžička 2002), namely Thanatus arenarius L. Koch, 1872, Thanatus atratus Simon, 1875 and Thanatus formicinus (Clerck, 1757). We measured and compared the body size (carapace length) and (pre-)epigyne height (length of the epigynal slits) of the material coming from the north Pannonian region (south Moravia and south Slovakia) where the type locality of Thanatus aridorum is located.

Material examined. Thanatus atratus: CZECHIA, 2 ♀♀, 1 subadult ♀, Mohelno, 20. Jun., coll. František Miller in NMPC, P6A-701/39; 1 ♀, 3 subadult ♀♀, Pavlov, 15. Jun. 1956, coll. František Miller in NMPC, P6A-701/42; SLOVAKIA, 3 ♀♀, 3 subadult ♀♀, Štúrovo, 10. Jun. 1956, coll. František Miller in NMPC, P6A-701/55.

Thanatus arenarius: CZECHIA, 3 ♀♀, 2 subadult ♀♀, Pouzdřany, 20. May 1965, coll. František Miller in NMPC, P6A-701/6; 1 subadult ♀, Pouzdřany, 5. May, coll. František Miller in NMPC, P6A-701/9; 1 subadult ♀, Pavlov, coll. František Miller in NMPC, P6A-701/4; 1 subadult ♀, Vranov, 10. Oct., coll. František Miller in NMPC, P6A-701/12.

Thanatus formicinus: CZECHIA, 1 subadult ♀, Říčky, Aug., coll. František Miller in NMPC, P6A-701/32; 4 ♀♀, 3 subadult ♀♀, Dráchov, 30. May, coll. František Miller in NMPC, P6A-701/17.


The type specimen re-examined here is faded and shrunken (probably after temporarily drying out), but it otherwise corresponds well to the original illustration (Fig. 1a). The carapace length is 2.8 mm, width 2.5 mm. The length of the first pair of legs is 9.4 mm (coxa 0.9, trochanter 0.4, femur 2.4, patella 1.2, tibia 1.9, metatarsus 1.4, tarsus 1.2). Also the “epigyne” in the slide (Fig. 1c) corresponds well to the original description (Fig. 1b). However, in contrast to the author of the original description, we consider it to be a pre-epigyne of a subadult female – it is small relative to the body size (epigynal slit length 0.14 mm, distance of the epigynal slits in the middle 0.11 mm; the ratio epigynal slit length/ carapace length = 0.05), and the spermathecae are not developed. In adult Thanatus females, the epigyne is larger relative to the body size (the ratio epigynal slit length/carapace length in T. arenarius is 0.12–0.13, in T. atratus 0.14–0.17, and in T. formicinus 0.13–0.16). We therefore conclude that Thanatus aridorum (Šilhavý, 1940) is a junior synonym of Thanatus formicinus (Clerck, 1757), new synonymy.

Fig. 1.

Thanatus aridorum Šilhavý, 1940, type specimen. a. figure of habitus from the original description (Šilhavý 1940); b. figure of epigyne from the original description (Šilhavý 1940); c. epigyne, ventral view; d. habitus, dorsal view; e. habitus, ventral view; f. slide with mounted “epigyne” and original labels written by V. Šilhavý



Seven species of the genus Thanatus occur in Czechia: Thanatus arenarius L. Koch, 1872, Thanatus atratus Simon, 1875, Thanatus formicinus (Clerck, 1757), Thanatus pictus L. Koch, 1881, Thanatus sabulosus (Menge, 1875), Thanatus striatus C. L. Koch, 1845 and Thanatus vulgaris Simon, 1870 (Buchar & Růžička 2002, Růžička & Buchar 2008, Řezáč et al. 2021). The Mohelenská hadcová step National Nature Reserve is one of the arachnologically best-investigated sites in Czechia (Buchar 1997). Four species of the genus Thanatus have been recorded from the site: T. arenarius (Fig. 2a), T. atratus (Fig. 2b), T. formicinus (Fig. 2c) (see Buchar 1997, Kůrka 1997, Buchar & Růžička 2002) and T. aridorum (Šilhavý 1940). The only specimen of T. aridorum that has ever been found is a subadult female that obviously belongs to one of the other three species known from this site. Also, in similar habitats in Baden-Württemberg (Badberg, Kaiserstuhl) only the two species, T. arenarius and T. formicinus, have been found (Bauer & Höfer 2017). It is probably neither T. arenarius nor T. atratus, as these species are smaller (Logunov 1996). On the other hand, the body size corresponds well to the body size of T. formicinus subadult females (Tab. 1). Concerning pre-epigyne morphology, the parallel slits resemble those in T. formicinus and T. arenarius (Fig. 2d, f), rather than the diverging ones in T. atratus (Fig. 2e, j). Comparing T. formicinus and T. arenarius, it is closer to T. formicinus (Fig. 2f), where the sclerotized pockets, visible under transparent cuticle, run deeper to the sides than in T. arenarius (Fig. 2d).

Fig. 2.

Subadult females of three species of Thanatus. a, d. Thanatus arenarius, subadult female, Czechia: Pouzdřany; b, e. Thanatus atratus, subadult female, Slovakia: Štúrovo; c, f. Thanatus formicinus, subadult female, Czechia: Dráchov. a-c. habitus, dorsal view; d-f. pre-epigyne, dorsal view, scale bar 100 µm


The immature epigyne irregularly present in subadult females of some spider species (e.g. in Eresoidea, Lycosoidea, Dionycha) has been a source of confusion in many taxonomic studies. For example, the type specimen of Storkaniella janinensis Kratochvíl & Miller, 1940 appeared to be a subadult female of Adonea fimbriata Simon, 1873 (Miller et al. 2012).

Tab. 1:

Carapace lengths of the adult and subadult females of the three Thanatus species occurring at the type locality of Thanatus aridorum. The measured material comes from the north Pannonian region (south Moravia and south Slovakia). Measurements are in mm. The only interval to which the carapace length of the type specimen of Thanatus aridorum fits (2.8 mm) is marked in bold


After his short interest in spiders, Vladimír Šilhavý focused on harvestmen. Despite being an amateur (he was a medical doctor), he became one of the greatest experts in opilionology (Pinto-da-Rocha et al. 2007). Among other topics, he invested great efforts to describe juvenile stages of central European harvestman species in particular (Šilhavý 1948, 1956). However, at the time when he found and described T. aridorum, he was still in his twenties and had only just started to gain experience in arachnology.


We thank Petr Dolejš for finding, loaning and measuring the type material of Thanatus aridorum and the Thanatus material for comparison, Simeon Indzhov, Carmen Urones and Éva Szita for comments and Ondřej Vaněk for help with the photographs. MŘ was supported by the Ministry of Agriculture of the Czech Republic (MZe RO0418). VR was supported by the institutional project RVO: 60077344.



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Milan Řezáč and Vlastimil Růžička "Thanatus aridorum Šilhavý, 1940 from Czechia is a junior synonym of Thanatus formicinus (Clerck, 1757) (Araneae: Philodromidae)," Arachnologische Mitteilungen: Arachnology Letters 63(1), 15-18, (26 August 2022).
Accepted: 7 February 2022; Published: 26 August 2022
new synonymy
subadult female
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