Nanometa, SIMON, 1908

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 : 786-788

NANOMETA SIMON, 1908 ( FIGS 4F , 87–91 )

Type species: Nanometa gentilis Simon, 1908 . The type specimen of N. gentilis is a female from Western Australia deposited at the Museum National d’Histoire Naturelle, Paris (examined).

Diagnosis: Nanometa can be distinguished from other tetragnathids by the following combination of characters: small size (body length c. 3–4 mm); abdomen covered with silver guanine patches; ramified median tracheal trunks ( Fig. 87B–D ); absence of femoral trichobothria; denticles between the cheliceral fang furrows ( Fig. 87D ); flat epigynum ( Fig. 89A ); copulatory ducts modified as sacs and separated from the spermathecae ( Figs 89B, D , 91C ); male book lung with a stridulatory file ( Fig. 87A ); male coxa IV mesal surface with cusps ( Fig. 88F ); cheliceral ectal margin rugose and dimorphic (the female cheliceral surface is smooth, Fig. 88A, E ); and cymbial ectobasal process and cymbial ectomedian process present ( Fig. 90A, C ). Description: Female: cephalic fovea absent ( Fig. 88B ). Ocular area higher than carapace lateral margins ( Fig. 88A ). Labium trapezoidal, wider than long and rebordered; sternum longer than wide ( Fig. 88C ). Anterior surface of chelicerae smooth; cheliceral boss present ( Fig. 88A ). Eyes subequal in size, juxtaposed, and on a tubercle ( Fig. 88A ). Secondary eyes with canoe-shaped tapetum. Clypeus height approximately one AME diameter. Booklung cuticle smooth. Tracheal spiracle located near the spinnerets, without accessory glands ( Fig. 87C ). ALS with c. 30 piriform spigots. PLS and PMS with c. eight aciniform spigots. PLS distal end of aggregate spigots embracing tip of flagelliform spigot ( Fig. 87H ). Epigynal plate flat, copulatory openings ventrally orientated and in the shape of pits ( Fig. 89A ). Spermathecae walls well sclerotized, fertilization ducts short and slightly curved ( Figs 89B , 91C ). Accessory gland openings grouped on a common pit near the spermatheca ducts junction ( Fig. 89B–D ).

Male: body length and cephalothorax morphology as in the female, except that the anterior cheliceral cuticle is rugose and the booklung covers have an stridulatory organ ( Figs 87A , 88E ). PLS triplet reduced to nubbins ( Fig. 87G ). Epiandrous fusules concentrated in two groups and immersed in pits ( Fig. 87E ). Palpal patella without macrosetae, palpal tibia slightly longer than wide ( Fig. 90A, D ). Paracymbium very small, smaller than the cymbial ectobasal process ( Fig. 90E ). Tegulum wider than long, spherical to oval ( Fig. 91A ). Conductor edges well sclerotized and fused to the tegulum; centre of conductor membranous (it expands when repeatedly transferred between KOH 10% and distilled water; Fig. 91A ). Embolic apophysis without processes; embolus and its base continuous and well sclerotized ( Fig. 91A ). Sperm duct spiralled without switchbacks.

Natural history: Nanometa is a monotypic genus endemic to Australia ( Platnick, 2009); however, at least 20 more species from Australia (including Tasmania) remain to be described (Ray Forster, unpubl. data). These spiders build horizontal webs with c. 16 spirals, c. 16 radii, and open hubs ( Fig. 4F ). They are found in forests building their webs in the low vegetation.

Taxonomy: Nanometa has never been revised, and new species wait to be described ( Forster & Forster, 1999). The specimens studied for the diagnosis and description belong to an undescribed species morphologically similar to N. gentilis , which we have also coded in the phylogenetic analysis. Davies (1988: fig. 17) illustrated another undescribed Nanometa species similar to the one that we examined. The anatomy of Nanometa is similar to that of the specimens referred in the text as ‘Nanometine sp.’; however, this latter undescribed species differs considerably in size (7.0 mm body length, in comparison with Nanometa , which is 4.0 mm). This ‘ Nanometinae sp.’ is similar in size to that illustrated by Davies (1988), also from Queensland, and referred there as ‘Metine sp.’ ( Davies, 1988: fig. 17), and the same species as ‘metaine from Australia’ in Álvarez-Padilla et al. (2009). We decided to leave this species unnamed until its phylogenetic placement is resolved using a larger taxonomic sample of Nanometinae . The morphology plus behaviour data set recovered Nanometa as sister to ‘ Orsinome ’ sarasini ( Fig. 144 ); when these data are combined with the DNA sequences, Nanometa is placed as sister to ‘ Nanometinae sp.’ ( Fig. 143A, B ).

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 87. Nanometa sp. abdomen: A, male book cuticle. B, abdomen tracheal system dorsal view. C, tracheal spiracle posterior view. D, median tracheae ramifications. E, epiandrous fusules. F, lateral trachea tip. G, male posterior lateral spinnerets. H, female spinnerets. All images from SEMFAP048.

Figure 88. Nanometa sp. cephalothorax: A, female tangential view. B, female dorsal view. C, female ventral view. D, female cheliceral denticles. E, male chelicera. F, male IV coxae dorsal view. All images from SEMFAP048.

Figure 89. Nanometa sp. epigynum: A, ventral view. B, dorsal view. C, accessory glands. D, spermatheca and copulatory ducts. All images from SEMFAP048.

Figure 90. Nanometa sp. male pedipalp: A, dorsal view. B, apical view. C, ventral view. D, ectal view. E, cymbial ectobasal process. F, mesal view. All images from SEMFAP048.

Figure 91. Nanometa sp. and ‘Orsinome’ sarasini genital anatomy illustrations: A, Nanometa sp. palp expanded. B, ‘Orsinome’ sarasini, pedipalp expanded. C, Nanometa sp. cleared epigynum ventral view. D, ‘Orsinome’ sarasini cleared epigynum ventral view.

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.