Mesida, KULCZYNSKI, 1911

Álvarez-Padilla, Fernando & Hormiga, Gustavo, 2011, Morphological and phylogenetic atlas of the orb-weaving spider family Tetragnathidae (Araneae: Araneoidea), Zoological Journal of the Linnean Society 162 (4), pp. 713-879 : 770-772

MESIDA KULCZYŃSKI, 1911 ( FIGS 4A , 51–55 )

Type species: Mesida humilis Kulczyński, 1911 . Type specimen a female from Papua New Guinea, depository unknown .

Diagnosis: Mesida species are very similar to those of Leucauge but can be distinguished from the latter and from all other tetragnathids by the following combination of characters: two parallel rows of feathered trichobothria on the femora IV ectal surface ( Fig. 61H ); copulatory and fertilization ducts running parallel before entering the spermathecae ( Figs 43E , 55D ); flat epigynal plate with a round atrium ( Fig. 53A, B ; Chrysanthus, 1975: fig. 6); male cheliceral anterior surface with a median spur ( Fig. 52E ; Chrysanthus, 1975: fig. 7); and the presence of a cymbial dorsobasal process ( Fig. 54C, D ).

Description: Female: body length c. 7.0 mm. Cephalothorax fovea formed by two short longitudinal pits, carapace cephalic area almost as wide as thoracic area ( Fig. 52C ). Ocular area lower than carapace lateral margins ( Fig. 52B ). Labium trapezoidal, wider than long and rebordered. Sternum as wide as long ( Fig. 52A ). Anterior surface of chelicerae smooth; boss present ( Fig. 52D, E ). Secondary eyes with canoeshaped tapetum. Eyes subequal in size, lateral eyes slightly smaller, juxtaposed, and on a tubercle. Clypeus less than one AME diameter. Abdomen longer than wide, covered with silver guanine patches, some species such as Mesida argentiopunctata have a caudal abdominal tubercle. Booklung cuticle smooth. Tracheal spiracle near the spinnerets, with few accessory glands ( Fig. 51C ). Median tracheae not ramified, with rounded tips ( Fig. 51B, D, F ). ALS with c. 60 piriform spigots. PMS with three aciniform spigots between the cylindrical and minor ampullate silk gland spigots but without any aciniform spigots over the anterior surface. PLS with c. 20 aciniform spigots roughly arranged in two parallel lines, distal end of the aggregate spigots embracing the distal end of the flagelliform spigot ( Fig. 51E ). Epigynal plate flat, copulatory openings ventrally orientated and in the shape of longitudinal grooves ( Fig. 53A, B ). Spermathecae walls weakly sclerotized ( Fig. 53C ). Copulatory ducts more than half the spermathecae length but less than its total length, cuticle weakly sclerotized ( Fig. 53C ). Fertilization ducts coiled and sclerotized at their distal end ( Fig. 55D ). Accessory glands concentrated over the ducts, with their bases slightly wider than the duct ( Fig. 53D–F ).

Male: size and somatic morphology similar to that of the female, except that the cheliceral anterior surface cuticle is rugose, with a dorsal apophysis ( Fig. 52E ). Epiandrous plate well sclerotized, posterior margin thicker than the anterior margin ( Fig. 51G ); fusules immersed in a transverse groove, their bases wider than the fusule shaft. PLS triplet reduced to nubbins. Male palpal patella with one macroseta. Paracymbium hook-shaped, without apophyses and considerably shorter than the cymbium length ( Fig. 54F ). Tegulum roughly oval, with an ectal depression produced by the displaced subtegulum ( Fig. 54B ). Conductor rigid, with sclerotized edges although some parts are weakly sclerotized. Conductor-tegulum attachment membranous, originating at the ventral edge of the tegulum ( Figs 54B , 55B ). Embolus base rectangular, longer than wide ( Fig. 55A ). Embolus flexible and weakly sclerotized. Sperm duct path convoluted with several coils ( Fig. 55C ).

Natural history: This genus includes 12 species and one subspecies, all with an Australasian distribution ( Chrysanthus, 1975; Davies, 1988; Barrion & Litsinger, 1995; Zhu et al., 2003). Mesida argentiopunctata builds vertical webs with c. 20 radii, fewer than c. 20 spirals and open hubs ( Fig. 4A ). These webs are usually found on the forest lower vegetation. The biology of Mesida remains largely unknown. A recent study comparing the spider communities between habitats with different levels of disturbance found that Mesida gemmea ( Hasselt, 1882) and Leucauge argentina ( Hasselt, 1882) were the most abundant species in primary forest on the Orchid Island, south of Taiwan ( Chen & Tso, 2004).

Taxonomy: Mesida has never been revised. Our description and diagnosis is based on specimens of M. argentiopunctata and the species descriptions and illustrations of M. humilis by Chrysanthus (1975). The best documented species of this genus is M. argentiopunctata , which we have coded in our character matrix. It is possible that Mesida is a clade within Leucauge or paraphyletic in relation to this latter genus (although Leucauge ’s monophyly has not been tested in sufficient depth). Several Asian species of Leucauge share many diagnostic characters with Mesida , such as the long and perpendicular cymbial dorsobasal process ( Song et al., 1999: fig. 122A–N). Tanikawa (2001) proposed that Mesida and Tylorida were sister taxa based on one synapomorphy, the presence of a spur on the male chelicera ( Fig. 52H ). In Tanikawa’s analysis Mesida was represented by two species: M. argentiopunctata plus one unidentified species ( Tanikawa, 2001: fig. 141B). The cladistic analysis of Álvarez-Padilla (2007: fig. 142B) recovered Mesida and Opadometa as sister taxa based on one synapomorphy, the male chelicerae proportionally larger than the female chelicerae. The analyses of both our data sets (morphology plus behaviour and morphology plus behaviour plus DNA sequences) recovered Mesida as sister to a clade that includes Opadometa plus Leucauge ( Figs 143A , 144 ).

Figures

Figure 4. Webs of tetragnathids: A, Mesida argentiopunctata from Noosa National Park, Australia (37 cm horizontal) (Leuc004b). B, Metabus ebanoverde from Ébano Verde Natural Reserve, Dominican Republic (72 cm horizontal) (DSCN7567). C, Meta menardi from Zealand, Denmark (15 cm horizontal, photograph by Nikolaj Scharff). D, Metleucauge eldorado from California, USA (40 cm horizontal). E, Mollemeta edwardsi from Puyehue National Park, Chile (50 cm horizontal). F, Nanometa sp. from Lamington National Park, Australia (18 cm horizontal) (DSCN0492). Photographs (D) and (E) by Gustavo Hormiga.

Figure 43. Leucauge venusta epigynum: A, ventral view. B, spermatheca lateral view. C, spermatheca dorsal view. D and E, copulatory and fertilization ducts. F, accessory glands. All images from SEMFAP033.

Figure 51. Mesida argentiopunctata abdomen: A, tracheal spiracle and colulus. B, tracheal system dorsal view. C, tracheal spiracle posterior view. D, lateral tracheae cuticle. E, posterior lateral spinnerets. F, median tracheae. G, epiandrous fusules; insert, detail of fusules. Images (A–E) from SEMFAP061, (G) from SEMFAP037.

Figure 52. Mesida argentiopunctata cephalothorax: A, female cephalothorax ventral view and sternum. B, female tangential view. C, female dorsal view. D, female chelicera. E, male chelicera. F, male cephalothorax dorsal view. G, female femur IV trichobothria. H, male tangential view. Images of female specimens from SEMFAP061, male images from SEMFAP037.

Figure 53. Mesida argentiopunctata epigynum: A, posterior view. B, ventral view. C, dorsal view. D, accessory glands. E and F, copulatory and fertilization ducts. All images from SEMFAP061.

Figure 54. Mesida argentiopunctata male pedipalp: A, apical view. B, ventral view. C, cymbial dorsobasal process. D, pedipalp dorsal view. E, mesal view. F, ectal view. All images from SEMFAP037.

Figure 55. Mesida argentiopunctata genital anatomy illustrations: A and B, male pedipalp expanded. C, pedipalp bulb cleared ventral view. D, cleared epigynum dorsal view.

Figure 61. Metabus ocellatus abdomen: A, cuticle of the abdomen, close up of median lateral section. B, booklung external cuticle. C and D, median tracheae tip. E, tracheal system dorsal view. F, tracheal spiracle posterior view. G, epiandrous fusules. All images from SEMFAP036.

Figure 143. Strict consensus trees of parsimony analyses of the morphological and behavioural data set presented in Appendix 2: A, strict consensus cladogram of the five cladograms of minimal length obtained under equal weights of 1033 steps (consistency index = 26, retention index = 58); the consensus tree is ten steps longer. Bremer support values are given under the nodes. B, strict consensus of 11 optimal cladograms obtained with implied weights at concavities 1 to 100; the consensus tree is 101 steps longer than the equal weighted optimal cladograms. Symmetric resampling support values above 51% are given under each node. See text for additional details.

Figure 144. Preferred optimal cladogram from the study of Álvarez-Padilla et al. (2009). This tree is based on a combined analysis, using direct optimization methods, of multigene DNA sequences and the morphological and behavioural data set presented in Appendix 2. The single most parsimonious tree was 54 536 steps when all the data were analysed simultaneously. Numbers under each node correspond to the node numbers in Table 1 where all support values are plotted and the synapomorphies mapped.