Mesida KULCZYNSKI 1911
Creators: name: Álvarez-Padilla, Fernando
name: Hormiga, Gustavo
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Araneae
Tetragnathidae
Mesida

description: 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).
description: Published as part of Álvarez-Padilla, Fernando & Hormiga, Gustavo, 2011, Morphological and phylogenetic atlas of the orb-weaving spider family Tetragnathidae (Araneae: Araneoidea), pp. 713-879 in Zoological Journal of the Linnean Society 162 (4) on pages 770-772, DOI: 10.1111/j.1096-3642.2011.00692.x, http://zenodo.org/record/5440885