Plebs, Joseph & Framenau, 2012

Joseph, Mathew M. & Framenau, Volker W., 2012, Systematic review of a new orb-weaving spider genus (Araneae: Araneidae), with special reference to the Australasian-Pacific and South-East Asian fauna, Zoological Journal of the Linnean Society 166 (2), pp. 279-341 : 293-295

PLEBS GEN. NOV.

GRASS ORB- WEAVERS, GRASS ORB- WEAVING SPIDERS

Type species: Epeira eburna Keyserling, 1886 (designated here).

Diagnosis: Members of Plebs have previously been included in Zilla and Eriophora . They share with Zilla somatic similarities, but differ distinctly in genitalic characters, in particular the presence of a paramedian apophysis in the male pedipalp (e.g. Tanikawa, 2000). Hence, Plebs share a typical ‘eriophorine’ genital morphology that includes a paramedian apophysis and an elongated transverse median apophysis. Females have an elongated scape without terminal pockets. Plebs share this morphology with many other Australian genera such as Backobourkia , Acroaspis, Larinophora , and a number as of yet undescribed genera, of which species are placed in Araneus and Eriophora . However, Plebs differ from all other ‘eriophorines’ by a unique ventral pattern on the abdominal venter, i.e. a light inverted U-shaped pattern and two additional light spots anterolateral to the spinnerets ( Fig. 3 ). Plebs are unique within the Australasian/Pacific and Asian ‘eriophorine’ orbweaving spiders by including a vertical stabilimentum in their web (e.g. Bruce et al., 2004) (see also Fig. 1F ). Similar to other araneid spider genera with stabilimenta, Plebs are predominantly diurnal in contrast to most other araneines that are mainly active at night.

Description: Very small to medium-sized orb-weaving spiders; males (total length approximately 1.2–6.1) overall smaller than females (total length approximately 3.4–13.3). Carapace orange- to reddish-brown, slightly longer than wide, pear-shaped in dorsal view; surface generally glabrous but with some white setae mainly in cephalic region and along lateral margins; fovea variable (cross-shaped, Y-shaped, or longitudinal). Eyes: median ocular quadrangle rectangular ( P. eburnus , P. bradleyi , females of P. arleneae , P. cyphoxis , P. neocaledonicus , and P. patricius ) or trapezoidal and then wider anteriorly than posteriorly ( P. arletteae , P. salesi , P. opacus , P. rosemaryae , males of P. arleneae , P. cyphoxis , P. neocaledonicus , P. patricius , and P. sebastiani ); lateral eyes nearly touching; posterior eye row slightly recurved in both males and females. Chelicerae orange- to reddish-brown; few darker setae medially in apical half; four promarginal and three retromarginal teeth. Endite maxillae with serrated anterior margin ( Fig. 4E, F ). Labium triangular, dark reddish-brown; distal margin white with a few dark brown setae centrally at the distal tip. Sternum: orange-brown, with scattered dark pigmentation, sparsely covered with white setae and brown bristles. Leg formula 1> 2> 4> 3 (males of all species and females of P. cyphoxis , P. rosemaryae , and P. arleneae ) or 1423 (all females except P. cyphoxis , P. rosemaryae , and P. arleneae ); yellow-brown with dark annulations; leg spination variable; males with coxal spur on leg 1 with corresponding femoral groove on leg 2; male coxae 4 with two to three stout setae ventrally (absent in P. patricius and P. arleneae ). Abdomen generally glabrous, with a sparse cover of white setae; shape variable from subtriangular to elongated, generally longer than wide; general coloration off-white with a greenish-brown, marmorated folium. Venter with greenish-brown pigmentation; centrally with an inverted U-shaped white pattern and two white spots anterolateral to the spinnerets (more prominent in females). Spinnerets (based on female of P. eburnus ; Fig. 5A–D ) (nomenclature after Coddington, 1989: ALS with a large field of PI and one MAP accompanied by a small n ( Fig. 5B ). PMS with an anterior field of AC, a central CY and a posterior mAP accompanied by a posterior n ( Fig. 5C ). PLS with an widespread field of AC, an anterior CY, two long AG with a narrower FL in a triad, and a CY posteriorly. Male pedipalp patella with a single macroseta; paracymbium simple and generally rounded (with a curved tip in P. patricius ); tegulum with a small apical protrusion ( Fig. 4B ); median apophysis either with a narrowing or widening apex and with an arch over the radix at the base; embolus generally stout with a sickleshaped tip, often somewhat bulbous at base; terminal apophysis fleshy, with a sinuous base and a marginally sclerotized or unsclerotized tip; conductor of variable shape, sometimes with sclerotized tip; paramedian apophysis a basal outgrowth of the conductor, the tip spatulate and bent ventrally with a scaly texture in P. eburnus ( Fig. 4B, C ). Female epigyne of variable shape; scape generally elongated or tongue shaped and without distal cup; scape frequently torn off in P. patricius , P. arleneae , Plebs astridae , Plebs aureus , Plebs plumiopedellus , and Plebs yanbaruensis . Spermathecae spherical, elongate ovoid, elongate kidney-shaped or pear-shaped; sperm ducts with a single twist.

Phylogenetics: Plebs species have a single unambiguous synapomorphy, the light inverted U-shaped ventral pattern of the abdomen with two additional white spots anterolateral of the spinnerets (e.g. Figs 1B , 7B, D ). The sister genus to Plebs in our analysis is Novakiella , their monophyly supported by the female leg formula (character 31) and a diurnal activity pattern (character 35). Basal taxa in our analysis are from Australia and the Pacific region with a derived clade of Asian species, suggesting a Gondwanan origin of Plebs .

Composition: Twenty-two species ( Table 4).

Distribution: Asia ( China, India, Japan, South and North Korea) (as Eriophora reported in, e.g. Song et al., 1999; Tanikawa, 2000; Chang & Tso, 2004; Zhang et al., 2006; Namkung et al., 2009), South-East Asia ( Philippines, Thailand), Australia and the Pacific region ( New Caledonia, Vanuatu) (this study).

Etymology: The genus-group name is of Latin origin meaning ‘common people’ and refers to the common occurrence of the species of this genus, in particular in Australia. The gender is masculine.

Figures

Figure 1. Plebs species. A–C, Plebs eburnus comb. nov. A, female from The Gap, Brisbane, Queensland; B, female from The Gap, Brisbane, Queensland – ventral view to illustrate the distinct square, U-shaped pattern on the abdomen characteristic of the genus; C, male from The Gap, Brisbane, Queensland. D, Plebs bradleyi comb. nov. from Wombolano Park, Heathmont, Victoria. E–G, Plebs cyphoxis comb. nov. E, female from Sterling Range National Park, Western Australia; F, female from Boya, Perth, Western Australia – on web to illustrate stabilimentum; G, Habitat of female from Boya, Perth, Western Australia. Photographs: Volker Framenau, Robert Whyte, Mathew M. Joseph.

Figure 3. Phylogenetic hypothesis for Plebs within a taxon sampling of Australian ‘eriophorine’ orb-weaving spiders (Araneidae) (length = 114, consistency index = 0.38, retention index = 0.72). Full circles indicate unambiguous synapomorphies and open circles homoplasious character state changes. Character numbers (above circles) and states (below circles) as in Table 1. The topology only shows unambiguous character state changes. Bremer support values are given in circles below branches.

Figure 4. Scanning electron micrographs of Plebs eburnus comb. nov. A–C, male from Atherton Tablelands, Queensland. A, right coxa 4 showing coxal setae; B, expanded left pedipalp; C, right pedipalp close-up showing paramedian apophysis. D, E, female from Atherton Plateau, Queensland (ZMUC 12286). D; epigyne. E, ventral view of fang and teeth. F, close-up of right maxilla; G, frontal view of eye group. Abbreviations: AR, arch of median apophysis; CS, coxal setae; CO, conductor; CY, cymbium; EM, embolus; MA, median apophysis; PMA, paramedian apophysis; RA, radix; TA, terminal apophysis; TP, tegular protrusion.

Figure 5. Scanning electron micrographs of the spinnerets of Plebs eburnus comb. nov. – female from Atherton Plateau, Queensland (ZMUC 12286). A, spinneret group; B, close-up of right anterior lateral spinneret; C, close-up of posterior median spinnerets; D, close-up of right posterior lateral spinneret. Abbreviations: AC, aciniform gland spigot; AG, aggregate gland spigots; ALS, anterior lateral spinneret; CY, cylindriform gland spigot; FL, flagelliform gland spigot; MAP, major ampullate gland spigot; mAP, minor ampullate gland spigot; n, nubbin; PI, piriform gland spigots; PLS, posterior lateral spinneret; PMS, posterior median spinneret.

Figure 7. Plebs eburnus comb. nov. A, B, female from Warrandyte State Park, Victoria (WAM T84324). A, dorsal view; B, ventral view. C, D, female from Atherton Talbelands, Lake Tinaroo, Queensland (ZMUC 12287). C, dorsal view; D, ventral view. E, female from Ku-Ring-Gai Chase National Park, McCarrs Creek, New South Wales (ZMUC 12274), dorsal view. F, female from Ku-Ring-Gai Chase National Park, Smiths Creek, New South Wales (ZMUC 12277), dorsal view. Scale bar = 2.0 mm.