Eresus Walckenaer

Miller, Jeremy A., Griswold, Charles E., Scharff, Nikolaj, Řezac, Milan, Szűts, Tamas & Marhabaie, Mohammad, 2012, The velvet spiders: an atlas of the Eresidae (Arachnida, Araneae), ZooKeys 195, pp. 1-144 : 40-41

Eresus Walckenaer

Eresus Walckenaer, 1805: 21. Type species Aranea cinnaberina Olivier, 1789.

Note.

Eresus contains 23 recognized species group names (including 6 subspecies) from the Mediterranean and temperate latitudes of Europe and Asia. We examined specimens of several species representing the two major morphological groups within the genus. Our first exemplar, Eresus walckenaeri , is a cohesive species, based on both morphological and molecular data ( Johannesen et al. 2005). Our specimens were from Bulgaria and Greece (Kresna, Bulgaria, MR; Pieria, Greece, MR020, MR; Lakonia, Greece, ZMUC 00012903, ZMUC). The primary types of Eresus walckenaeri are probably lost, but the original description and drawings, and our use in part of nearly topotypic material, allow us to identify this species with confidence. The second major group within the genus is a complex of closely related species including Eresus kollari (including the junior synonyms Eresus cinnaberinus and Eresus niger ) and Eresus sandaliatus (Martini & Goeze, 1778); we refer to this assemblage collectively as the Eresus sandaliatus group. The somatic description was based on specimens of Eresus kollari from Czechia (Srbsko, MR016, MR; Prague, MR007, MR); scanning electron micrographs of the male palp are from a specimen of Eresus kollari from Hungary (Remete Mountain, CASENT 9037134, CAS); scanning electron micrographs and some photographs of the female genitalia are from a specimen of Eresus sandaliatus from SE of Silkeborg, Denmark (CASENT 9039243, CAS). The spinneret spigot morphology of Eresus sandaliatus group species was described and scanned in Griswold et al. (2005: 24-27, figs 31-32, 33 A–F, 34 A–C). Řezáč et al. (2008) examined copious material from the Eresus sandaliatus group including one of the two syntypes of Eresus kollari .

We found no characters that clearly and simultaneously separate Eresus females from other eresid genera, despite support from molecular data for a monophyletic Eresus ( Miller et al. 2010a). Separate diagnoses for females of the two species groups appear in the following section.

Diagnosis.

Male Eresus are usually recognized by their distinctive dorsal abdominal pattern, which features two pairs of large round dark patches surrounding the first and second sigilla on a field of red setae, sometimes with a pair of smaller dark patches surrounding the third sigilla (Figs 2B, D, 40A, 43A); if with a black abdomen, then recognized by the distinctive notch on the embolic conductor (cf. Fig. 43J; note that black-abdomened form known as Eresus tristis Kroneberg, 1875 is currently cataloged as a synonym of Eresus kollari , but this is not accepted by all workers, e.g., Řezáč et al. 2008: 264, who noted that it is an "obviously different species"). Females of Eresus walckenaeri distinguished from other eresids except Dresserus and Gandanameno by the copulatory openings, which are broadly separated by hirsute cuticle (Figs 16G, 42B; separated by a glabrous median lobe in other eresids, e.g., Figs 16B, I, 29C, 45A), distinguished from Dresserus and Gandanameno by the more posterior position of the PLE (<0.28 in Gandanameno and Dresserus ,> 0.33 in Eresus walckenaeri ); females of the Eresus sandaliatus group distinguished from other eresids except Paradonea variegata by the large, bulbous spermathecal head (Figs 16K, L, 45 B–D), distinguished from Paradonea variegata by the smaller size difference between the AME and PME (AME/PME> 0.5 in Eresus sandaliatus group, Fig. 9C; <0.4 in Paradonea variegata , Fig. 10G) and by the overall darker color; thick stalks leading to the spermathecal head in some Stegodyphus species can be mistaken for large, bulbous spermathecal heads (Fig. 18J) although they are in fact compact sinuous ducts (Fig. 82B); Eresus sandaliatus group further distinguished from Stegodyphus by the more posterior position of the PLE (> 0.33 in Eresus sandaliatus group; <0.29 in Stegodyphus ).

Distinguishing species.

Male of Eresus walckenaeri distinguished from those of the Eresus sandaliatus group by the ribbon-like conductor with a blunt, rounded tip (Fig. 41C, D; notched in Eresus sandaliatus group, Fig. 44D, E) and the 1.5 helical turns of the embolus (ca. 1 helical turn in Eresus sandaliatus group). Various species within the Eresus sandaliatus group distinguished primarily by coloration and details of the conductor shape and vulva (Fig. 16H, I, K, L; see also Řezáč et al. 2008).

Natural history.

Known from various non-forest warm and dry habitats. Some species build a simple vertical burrow lined with silk. The opening is covered by silken sheet camouflaged from above by debris. Signaling threads radiate out from the edges of this roof. Some species (e.g., Eresus walckenaeri , Eresus crassitibialis Wunderlich) do not dig burrows; their silken tubes lie just under stones or on (Milan Řezáč, personal observation).