Tetragnathidae Menge, 1866

Dimitrov, Dimitar & Hormiga, Gustavo, 2009, Revision And Cladistic Analysis Of The Orbweaving Spider Genus Cyrtognatha Keyserling, 1881 (Araneae, Tetragnathidae), Bulletin of the American Museum of Natural History 2009 (317), pp. 1-140 : 30-35

Family Tetragnathidae Menge, 1866 Genus Cyrtognatha, Keyserling, 1881

Type species by original designation: Cyrtognatha nigrovittata, Keyserling, 1881 .

Agriognatha , O. P.- Cambridge, 1896, new synonymy.

DIAGNOSIS: Cyrtognatha can be easily distinguished from all other tetragnathids by the presence of a straight line of long and robust macrosetae with enlarged bases on the retrolateral surface of the posterior lateral spinnerets (fig. 28A, G, J). Such macrosetae are unique to this genus and are present in males, females, and juveniles. These macrosetae are relatively large and can be easily observed using a stereomicroscope, even at relatively low magnifications, which allows the correct genus determination of immature specimens. The shape of the female internal genitalia is also diagnostic for Cyrtognatha (fig. 7) (see also Dimitrov et al., 2007). In Cyrtognatha the spermathecae are reduced and the sperm storage function is taken by an unpaired membranous structure (the posterior sac). The presence of this structure seems to be unique and therefore diagnostic for this genus. Cyrtognatha species can also be distinguished from other tetragnathids by the shape of the male chelicerae, which are not projected but are wider distally and conspicuously divergent in the distal two-thirds (e.g., figs. 1A–C, 8E–G).

The enlarged and highly modified embolus is also diagnostic. While in most tetragnathids and all Tetragnathinae the embolus is a thin cylindrical tube, in Cyrtognatha the embolus is widened, often as wide as half of the tegulum diameter (e.g., C. insolita and C. morona , figs. 37A–C and 16A–C, respectively). Within Tetragnathinae , males of Cyrtognatha further differ from Pachygnatha and Tetragnatha by having the paracymbium attached to the base of the cymbium (in Pachygnatha and Tetragnatha the paracymbium is a separate sclerite connected to the cymbium by means of a membrane). Cyrtognatha can be also easily distinguished from Pachygnatha by the shape of the sternum (which does not surround the coxae; figs. 8G, 48A), and from Tetragnatha by the shape of abdomen, which in Cyrtognatha is less elongated and more oval in shape, and often with well-developed dorsal tubercles. Also, the chelicerae are not projected, and the conductor is more complex. An additional diagnostic character separating Cyrtognatha from Tetragnatha (and other closely related genera) is the presence in the former genus of feathered trichobothria on the femur of the fourth leg (figs. 29F, 36B, 54I). Such trichobothria are widespread among leucaugine genera, but in Cyrtognatha feathered and nonfeathered trichobothria are alternated. The first four or five trichobothria near the base of the femur have short ramifications (feathered trichobothria) (fig. 29F). They are followed by one trichobothrium, which is about twice as short and does not have such ramifications (smooth trichobothria). This nonfeathered trichobothrium is followed again by a feathered one, and this pattern is repeated (fig. 12H). Finally, Cyrtognatha also differs from other Tetragnathinae by its more complex conductor, which carries a very welldeveloped basal apophysis (fig. 6C) and an apical apophysis (fig. 6C–E).

DESCRIPTION: Small to medium size tetragnathid spiders; total body length 3.18–7.80 in males and 4.30–10.73 in females. Males slightly smaller than females. Carapace longer than wide, 1.47–3.10 long in males and from 1.75 to 3.90 long in females; light brown-yellowish to dark brown with a welldistinguished fovea. Sternum slightly longer than wide and prolonged between coxae IV. ALE on short lateral elevations and close to the PLE; AME and PME placed on the edges of an imaginary rectangle. AME on an elevation, often slightly higher in males. PME and AME slightly larger than the other eyes. Lateral eyes with nearly the same diameter. Clypeus height from one to twice the AME diameter in males. In females the clypeus is lower and its height ranges from 0.1 to 1.3 times the AME diameter. Labium trapezoidal, wider distally, dark in color, and almost as high as its maximum width. Endites elongated, divergent, and distally widened (figs. 29B, 35A, 38H). Chelicerae large and massive, sexually dimorphic, usually darker than the rest of the cephalothorax. Male chelicerae conspicuously divergent and not projected (e.g., figs. 1A–C, 38A–C; see also O.P.- Cambridge, 1896). The project- ed chelicerae relative to the cephalothorax is most likely a result of the dehydrating effect of alcohol and the resulting muscle contraction. The lack of observation in vivo, most likely, is the reason for describing the chelicerae of this genus as projected in the original description. Chelicerae distally wider and with a small cheliceral boss. Cheliceral fangs long, slightly curved, and with short retrolateral outgrowth (fig. 42B, D, E), which in some species can be smaller or absent (fig. 38B, F). Chelicerae distally with heavily sclerotized dorsal tooth close to the fang articulation (figs. 38E, 42E, H, 48H). In some species the dorsal tooth is reduced in size and it is similar to the distal teeth (e.g., C. pachygnathoides , fig. 26B). Distal margins of the chelicerae with three anterior and four posterior teeth. The number of cheliceral teeth does not usually vary between and within species and between males and females, but one specimen with five posterior teeth on one of the chelicerae was found in a male of C. petila (in this case the specimen had four teeth on the other chelicerae, and specimens from the same species had four teeth on both chelicerae as well). Female chelicerae are less divergent, without the distal tooth, cylindrical, and not widened distally; the teeth on the distal margin are closer to each other. Legs carry numerous setae and strong dark colored spines; legs slightly longer in males than in females (figs. 11H, 21A, B). Leg I is the longest and leg III is the shortest. Tarsus and distal part of the metatarsus without spines. Femur I length varies from 3.67 to 6.82 in males and from 1.86 to 5.88 in females. Abdomen elongated, longer than wide, of very variable coloration, from brownish with reflecting guanine spots and green and reddish tones to yellowish, almost totally covered with guanine causing silvery reflecting appearance (figs. 11H, 26A, C, D). Live specimens that were observed during this study presented distinct and more vivid coloration compared to specimens preserved in alcohol. Some of the pigments (especially the one responsible for the green coloration) are quickly degraded in alcohol and fade fast to brown-yellowish. Brownish pigments appear to be more resistant but also fade gradually with time. Abdomen dorsally with two lateral tubercles on its proximal edge (in some species these tubercles are reduced and the abdomen is just swollen proximally). Some species have a third distal caudal tubercle (e.g., figs. 30D, 63A–C). Height of distal tubercle varies greatly between and within species and in some cases it may be as high as or higher than the abdomen. Several species that lack a caudal tubercle have a distinctive abdominal tubercle placed dorsally, close to the half length of the abdomen (e.g., C. espanola , fig. 36F). Ventrally the guanine spots are fewer and smaller; in many species a darker band is present starting just after the genital opening.

Spinnerets: ALS with extensive piriform fields of more than 45 spigots (figs. 28A, B, 35C,G). PLS mesal cylindrical spigot peripheral (figs. 28A, C, G, 35F). PLS with a line of macrosetae on its retrolateral surface (figs. 28A, G, J, 35E–F; such a line of setae is unique to Cyrtognatha and is one of the most conspicuous synapomorphies of this genus). PLS with about 15–20 AC spigots (fewer in males) arranged roughly in two transversal lines. The two CY spigots are placed retrolaterally, one anterior and the other posterior to the AC lines. In females the AG–FL triplet is just anterior to AC and on the same line with the anterior CY spigot. Both AG spigots embrace the FL spigot and the three of them are placed in a fairly straight line (figs. 28C– E, G, J, 35E–F). Adult males lack the triplet (fig. 57C). PMS in females with a large CY spigot with modified setae near its base (figs. 28H, 36A) on the anterior edge; AC spigots (10 or fewer) forming a straight line between the CY and the medially placed mAP (figs. 28F, H, 36A). In males PMS does not have the CY spigot and the number of the AC spigots is less than in females (fig. 57B). In both males and females PMS have well-developed nubbin posteriorly to the mAP (figs. 57B and 28H, respectively).

Tracheal system simple (figs. 41H, I, 45E, F): Tracheal spiracle situated near the spinnerets. There are two shorter median and two longer lateral tracheae, which are not fused at the base and connect to an atrium that opens to a spiracle. The long pair of lateral tracheae enters the cephalothorax, while the short one barely reaches the anterior part of the abdomen. None of the tracheae has ramifications. The base of the tracheae carries numerous accessory glands (fig. 45G).

Male pedipalp (fig. 6): Tibia longer than wide, with six retrolateral trichobothria (figs. 8B, 37B) and long dark setae starting near its distal margin. Cymbium wider basally, elongated with swollen apex (figs. 13D, 27A, B, E, F). Base of the cymbium with a short conical apophysis, which seems to guide the movement of the paracymbium when the palp is expanded. Paracymbium almost straight or slightly curved with wider apex; not a separate sclerite, its inner part attached to the cymbium by a membrane, which allows certain mobility when filled with hemolymph (fig. 41D, F). Tegulum spherical. Embolus enlarged, often much larger than conductor. In some species the embolus has a subterminal enlargement of the spermatic duct (e.g., C. morona ; fig. 16A– C). Embolus base arising from center of tegulum and coiling then with conductor. Portion of the embolus enclosed in conductor varies between species but in all cases most of it is free (e.g., C. atopica and C. rucilla ; figs. 8A–C and 41A–C, respectively). Apical part of tegulum with a cuplike depression where the embolus and the conductor rest; the edge of this depression is slightly elevated, forming a small ridge. In some species this ridge is heavily chitinized and has brownish coloration. Apical part of the tegulum membranous, connecting to the embolus base and conductor by means of a membrane (this membranous connection allows limited mobility of the embolus and the conductor with respect to the tegulum). Sperm duct starts from the wide fundus and coils 1.5–2 times before exiting the tegulum near its center. The last half turn of the spermatic duct, just before exiting the tegulum, abruptly narrows, decreasing its diameter by more than two-thirds (figs. 6A, D, E, 41D–F, 62D).

Embolus in most of species with a very well developed and complex metine embolic apophysis (MEA, figs. 6A, B, D, 13A, C, F, 62D). A large and complex membrane is often present between the outer heavily chitinized part of the MEA and the embolus. In some species this membrane connects to the embolus near the base of the MEA and runs to its tip forming various folds (fig. 13A). Although most of the species have a MEA of varying complexity, in several species the embolus does not have any apophyses (e.g., C. rucilla and C. simoni ; figs. 41A–C, 43B, J, H and fig. 47A–C, respectively) or has small longitudinal ridges (e.g., C. paradoxa ; fig. 20A–C). In C. insolita the membrane between the MEA and the embolus is densely covered with short conical outgrowths (fig. 39I, J), giving this membrane a serrated appearance. Similar outgrowths, but with lower density and different shape, are found in other species (e.g., C. quichua , fig. 13F, I). Apical part of the embolus very variable across species and therefore useful for identification. Embolus tip always cylindrical, independent of the shape of the rest of the embolus. In some species the embolus tip carries a small membranous ridge (e.g., C. bella ; fig. 58A– C). In addition to this membranous ridge C. morona has also a short apophysis (fig. 16A– C).

Conductor (fig. 6) originating from the tegulum as a single lamina that bends toward the center of the tegulum and goes under the basal part of the embolus. In this area the conductor lamina has a long lamellar process, the basal conductor apophysis that runs apically over the tegulum and under the embolus (fig. 6C). Distal edge of basal conductor apophysis continues on prolateral side of embolus and turns apically. In many species the basal conductor apophysis ends with a well-developed membrane or with an incision that forms two processes. Distal to the base of the basal apophysis the conductor bends again but in the opposite direction, partially covering the embolus. The tip of the conductor in all species of the genus has a very characteristic semicircular apical apophysis (figs. 6A, C–E, 9A, 41A). Epiandrous fusules arranged in a line in a shallow invagination of the cuticle just over the male gonopore (figs. 38G, 55D). The number of fusules varies between species from 6 in C. insolita (fig. 38G) to 14 in C. bryantae (fig. 55D). The morphology of the epiandrous fussles in most Cyrtogantha species, however, remains unknown, and thus the variation may be wider.

Females lack epigynum. The opening of the female genitalia is formed by a fold of the abdomen cuticle that carries setae on its dorsal side (the actual genital opening is shifted to the end of this fold; fig. 7). Spermathecae absent or vestigial. The uterus externus connects via an enlarged chamber with a nonpaired membranous structure that has a posterior sac (a nonpaired sperm storage organ) (see also Dimitrov et al., 2007).

COMPOSITION: Cyrtognatha currently contains 21 species: C. nigrovittata Keyserling, 1881 , C. pachygnathoides (O. P.- Cambridge, 1894), C. bella (O. P.- Cambridge, 1896), C. serrata Simon, 1897 , C. lepida (O. P.- Cambridge, 1889), C. simoni ( Bryant, 1940) , C. rucilla ( Bryant, 1945) , C. espanola ( Bryant, 1945) , C. bryantae (Chickering, 1956) , C. insolita (Chickering, 1956) , C. catia , n. sp., C. atopica , n. sp., C. eberhardi , n. sp., C. quichua , n. sp., C. waorani , n. sp., C. morona , n. sp., C. leviorum , n. sp., C. petila , n. sp., C. paradoxa , n. sp., C. orphana , n. sp., and C. pathetica n. sp.

Most of the species are known from just a few specimens. Given the wide distribution of this genus and the lack of extensive sampling in most of the Neotropical cloud forests, these species most likely represent just a small fraction of the true diversity of Cyrtognatha .