Metellina, CHAMBERLIN & IVIE, 1941

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 : 779-782

METELLINA CHAMBERLIN & IVIE, 1941 ( FIGS 66–70 )

Type species: Metellina curtisi ( McCook, 1894) . The syntypes of Pachygnatha curtisi are fragments of three male specimens from California ( USA), deposited at the Academy of Natural Sciences , Philadelphia ( Levi, 1980) .

Diagnosis: Metellina species can be distinguished from all other tetragnathid genera by the following combination of characters: abdomen oval, longer than wide; secondary eyes with canoe-shaped tapetum ( Levi, 1980: figs 95, 96); PLE on a single tubercle ( Fig. 67C, E ); epigynal plate flat ( Fig. 68A, B ); copulatory openings posteriorly orientated ( Fig. 68D ); fertilization ducts originating on the anterior surface of the spermathecae ( Figs 68C , 70D ); accessory glands concentrated near the copulatory ducts ( Fig. 68F ); cymbial ectobasal process formed by a massive cuticular fold ( Fig. 69C, D ); cymbial ectomedian process absent ( Fig. 69D ); paracymbium slightly longer than half the cymbium length; and sperm duct without switch backs ( Fig. 70C ).

Description: Female: body length c. 8.0 mm. Cephalic fovea formed by a transverse, deep, M-shaped groove ( Fig. 67A ). Ocular area higher than carapace lateral margins ( Fig. 67C, E ). Labium trapezoidal, wider than long and rebordered. Sternum slightly longer than wide ( Fig. 67D ). Anterior surface of chelicerae smooth; boss present ( Fig. 67C, E ). Eyes subequal in size, lateral eyes slightly smaller, juxtaposed, and on a tubercle. Clypeus c. 1.5 times the AME diameter. Booklung cuticle smooth ( Fig. 66A ). Tracheal spiracle near the spinnerets. Median tracheae not ramified, longer than half the lateral tracheae length ( Fig. 66D ). Tracheal spiracle without accessory glands, median tracheae tips leaf-shaped ( Fig. 66C, F ). ALS with c. 60 piriform spigots ( Fig. 66B ). PMS with two aciniform spigots between the cylindrical and minor ampullate silk gland spigots but without any aciniform spigots over the anterior surface. PLS with more than 20 aciniform spigots, distal end of the aggregate spigots embracing the tip of flagelliform spigot. Epigynal plate flat, copulatory openings posteriorly orientated and in the shape of longitudinal grooves ( Fig. 68A, B, D ). Spermathecae walls well sclerotized ( Fig. 68C–F ). Copulatory and fertilization ducts cuticle well sclerotized. Copulatory ducts shorter than half the spermathecae length, fertilization ducts longer than the spermatheca width ( Figs 68F , 70D ). Accessory glands distributed on one side of the spermathecae, accessory gland openings arranged in groups ( Fig. 68E, F ).

Male: size and somatic morphology similar to that of the female, except the chelicerae are slightly larger and divergent ( Fig. 67B, C, F ). PLS triplet reduced to nubbins. Epiandrous plate flat, fusules arranged in two groups and immersed in pits ( Fig. 66E ). Palpal patella with one macroseta, palpal tibia slightly longer than wide. Tegulum wider than long and larger than the subtegulum. Conductor well sclerotized and fused to the tegulum ( Fig. 70B, C ). Embolic apophysis massive and square in ectal view; embolus short and well sclerotized ( Figs 69B , 70B ). Sperm duct spiralled ( Fig. 70C ).

Natural history: The Holarctic genus Metellina includes seven species and one subspecies ( Levi, 1980; Marusik, 1986). Metellina builds vertical webs with c. 25 radii, more than 30 spirals, and an open hub ( Levi, 1980: pl. 6). These spiders are found either in dark and humid places or amongst the forest low vegetation. A few aspects of the biology of M. segmentata have been studied, such as the reproductive biology ( Rubenstein, 1987; Prenter, Montgomery & Elwood, 1995; Hack, Thompson & Fernandez, 1997; Malakov, Bilde & Lubin, 2004), the phenology and life cycle, including that of Metellina mengei ( Blackwall, 1869; Toft, 1983), and the sperm ultrastructure and development ( Michalik, Sacher & Alberti, 2005).

Taxonomy: Metellina has never been revised, except for the North American species ( Levi, 1980). Our diagnosis and description includes the species revised by Levi (1980). We coded M. segmentata for the phylogenetic analysis. The monophyly of Metellina has never been tested. Two hypotheses exist regarding the sister group of Metellina , either sister to Chrysometa (supported by the chelicerae of

782 F. ÁLVAREZ-PADILLA and G. HORMIGA the male larger than those of the female and by having the sperm duct without switch backs; Hormiga et al., 1995); or sister to Dolichognatha ( Álvarez-Padilla, 2007) . The morphology plus behaviour data set recovered Metellina as sister to Dolichognatha ( Fig. 143A, B ); when these data are combined with DNA sequences, Metellina comes out as sister to a clade that includes Dolichognatha , Chrysometa , and Diphya ( Fig. 144 ).

Figures

Figure 66. Metellina segmentata abdomen: A, booklung external cuticle. B, anterior lateral spinnerets; arrow in insert indicates the space between the piriform spigot bases and the spigot shaft. C, tracheal spiracle posterior view. D, tracheal system dorsal view. E, epiandrous fusules. F, median trachea tip. All images from SEMFAP044.

Figure 67. Metellina segmentata cephalothorax: A, female dorsal view. B, male dorsal view. C, male tangential view. D, female cephalothorax ventral view and sternum. E, female tangential view. F, female chelicera. G, male chelicera. H, female femur IV dorsal. All images from SEMFAP044.

Figure 68. Metellina segmentata epigynum: A, ventral view. B, lateral view. C, dorsal view. D, posterior view. E, accessory glands. F, spermatheca, fertilization and copulatory ducts. All images from SEMFAP044.

Figure 69. Metellina segmentata male pedipalp: A, ventral view. B, apical view. C, dorsal view. D, ectal view. E, mesal view. F, paracymbium and cymbial ectobasal process. All images from SEMFAP044.

Figure 70. Metellina segmentata genital anatomy illustrations: A and B, male pedipalp expanded. C, pedipalp bulb cleared ventral view. D, cleared epigynum dorsal 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.