Crossopriza cylindrogaster Simon, 1907
Huber, Bernhard A., 2009, Life on leaves: leaf-dwelling pholcids of Guinea, with emphasis on Crossopriza cylindrogaster Simon, a spider with inverted resting position, pseudo-eyes, lampshade web, and tetrahedral egg-sac (Araneae: Pholcidae), Journal of Natural History 43 (39 - 40), pp. 2491-2523 : 2494-2502
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|Crossopriza cylindrogaster Simon, 1907|
Apart from the cylindrical abdomen, Simon’s (1907) description is largely restricted to the colour pattern which agrees well with that of the specimens described below. Nevertheless, material from the type locality should be checked to support the assignment of the new material to Simon’s species.
Easily distinguished from known congeners by the cylindrical abdomen ( Figures 15–19 View Figures 15–31 ), the coloration (very pale greenish when alive, with distinctive pattern of black spots ventrally on abdomen, Figures 1, 3 View Figures 1–6 , 19 View Figures 15–31 ), the male chelicerae (two pairs of apophyses, Figure 47 View Figures 45–49 ), and the male palp (procursus, bulb, Figures 45, 46 View Figures 45–49 ). The female genitalia are simple and barely sclerotized, but also distinctive (pair of pockets, internal structures, Figures 19 View Figures 15–31 , 48, 49 View Figures 45–49 , 58 View Figures 50–62 ).
Total body length 4.3, carapace width 1.2. Leg 1: 43.7 (11.2 + 0.5 + 10.6 + 20.1 + 1.3), tibia 2: 6.7, tibia 3: 4.5, tibia 4: 6.8, tibia 1 L/d: 92. Habitus as in Figures 15–17 View Figures 15–31 ; carapace pale ochre-yellow with some black lateral marks, clypeus with some small black specks below triads, chelicerae without dark marks, sternum with black marks at bases of coxae 2–4, slightly darkened medially, legs pale whitish-grey, with many small black marks distributed irregularly, patellae and tibia–metatarsus joints brown, abdomen pale ochre-grey, dorsally with large white spots in two bands, ventrally with distinctive pattern of black marks. Distance PME–PME 120 µm, diameter PME 145 µm, distance PME–ALE 65 µm, distance AME–AME 20 µm, diameter AME 120 µm. Each lateral eye accompanied by small “pseudo-eye” ( Figures 22 View Figures 15–31 , 56 View Figures 50–62 ; see later). Ocular area slightly elevated, thoracic furrow deep, restricted to central area of carapace ( Figure 50 View Figures 50–62 ), clypeus unmodified. Chelicerae as in Figure 47 View Figures 45–49 , two pairs of frontal apophyses, distal apophyses with one modified hair each; without stridulatory ridges. Sternum wider than long (0.95/0.65), unmodified. Palps as in Figures 45 and 46 View Figures 45–49 , coxa with retrolateral apophysis, trochanter unmodified, femur with retrolateral hump and ventral bulge distally, tibia almost globular, cymbium with several macrosetae, tarsal organ capsulate ( Figure 52 View Figures 50–62 ), procursus rather simple, only distally with some distinctive membranous and sclerotized elements ( Figures 53, 54 View Figures 50–62 ), bulb with short membranous embolus and basally attached to it a distinctive bulbal apophysis ( Figure 53 View Figures 50–62 ). Legs without spines and curved hairs, few vertical hairs; retrolateral trichobothrium on tibia 1 at 2%; prolateral trichobothrium present on all tibiae; tarsal pseudosegments very indistinct, only distally very few visible in dissecting microscope; tarsus 4 with two rows of comb-hairs prolatero-ventrally ( Figures 61, 62 View Figures 50–62 ). Anterior lateral spinneret ( ALS) with one widened, one pointed, and five cylindrically shaped spigots ( Figure 59 View Figures 50–62 ); posterior median spinneret ( PMS) with two small spigots. Gonopore with two epiandrous spigots ( Figure 51 View Figures 50–62 ).
Tibia 1 in six other males: 10.0–11.0 (mean 10.5). The extent of black pigment varies, may include large parts of chelicerae, clypeus and sternum, and larger parts of palps, but never dorsal side of abdomen.
In general similar to male, same colour pattern but usually with less black pigment; distance PME–PME almost as in males (110 µm); tibia 1 in 20 females: 7.2–8.7 (mean 7.9). Epigynum weakly elevated, barely sclerotized ( Figure 19 View Figures 15–31 ), with pair of pockets ( Figures 20 View Figures 15–31 , 48 View Figures 45–49 , 58 View Figures 50–62 ); internal genitalia as in Figures 21 View Figures 15–31 and 49 View Figures 45–49 . Spinnerets and spigots as in male ( Figure 60 View Figures 50–62 ).
In both sexes and in juveniles, each of the six lateral eyes is accompanied by a distinct elevation that has a characteristic golden shine ( Figures 22 View Figures 15–31 , 56 View Figures 50–62 ). Serial sections show that the tapetum extends into this elevation, lying close to the cuticle ( Figure 23 View Figures 15–31 ), which explains the strong reflectance of light. In contrast to the cuticle of the lenses which is smooth, the cuticle of the pseudo-eyes is strongly sculptured ( Figure 57 View Figures 50–62 ). Obviously, each “pseudo-eye” is just an elaboration of a lateral eye, and light enters this part only through the lens of the lateral eye. The function of these structures remains a mystery. Such pseudo-eyes seem to be widespread among the genera close to Crossopriza ( Holocnemus , Cenemus , Hoplopholcus , Stygopholcus , Smeringopus , Smeringopina ), but in most species they are very indistinct (B.A. Huber, unpublished data).
The resting position of C. cylindrogaster is extremely unusual: the dorsal side of the abdomen is pressed against the leaf, the prosoma is at a right angle to the abdomen and directed away from the leaf, the legs are in a more or less usual position (femora towards dorsal) except that they are all tightly pressed against the leaf and thus approximately in one plane ( Figure 1 View Figures 1–6 ). A comparable position has not to my knowledge been described in any other pholcid, but the Brazilian leaf-dwelling Mesabolivar luteus seems to have much the same resting position (see http://www.uni-bonn.de/∼bhuber1/pholcidae_photos.html). In C. cylindrogaster , the unusual position probably explains why most of the spider’s body but not the dorsal side of the abdomen is covered with small black marks. When disturbed, the spiders barely react. Only when the web is strongly moved or the spider itself touched does it assume a “normal” position (hanging upside down) and slowly walk away. I could never see the shaking or whirling so typical of many other long-legged pholcids.
The web resembles that of hypochilids, the “lampshade weavers” ( Figure 5 View Figures 1–6 ). It could actually be seen as a variant of the typical pholcid domed sheet where the apex of the dome is broadly connected with the underside of the leaf. The diameter of the web is unusually small, apparently reflecting the fact that the spider’s legs are to touch the wall of the lampshade. Figure 5 View Figures 1–6 shows a web where the silk lines were made visible by white powder, and where the lighting conditions were adjusted for this purpose. Usually, the web is barely visible with the naked eye, as shown in Figures 1 and 6. A View Figures 1–6 few webs were seen to contain large numbers of silk puffs ( Figure 2 View Figures 1–6 ). Such “ornaments” have been described previously in an unidentified Crossopriza species from Morocco ( Hajer and Reháková 2003), and in two species of the closely related genus Holocnemus ( Wiehle 1933; Sedey and Jakob 1998; Hajer and Reháková 2003). They also seem to occur in Hoplopholcus , another probably closely related genus (unpublished photo of H. minous (?) by John and Frances Murphy).
As in other pholcids ( Eberhard and Briceño 1983), males were often found to rest close to females ( Figure 6 View Figures 1–6 ). However, while in other pholcids male and female share the same web, C. cylindrogaster males build their own web close to the female web. Sharing a single web is apparently precluded by the small size of the web. Another common pholcid trait that is uniquely modified in C. cylindrogaster concerns the egg-sacs. As in all pholcids, females carry the egg-sac in their chelicerae until the spiderlings hatch and even a short while after that ( Figures 3, 4 View Figures 1–6 ). Only two females with egg-sacs were collected, and in both the shape of the egg-sac was a tetrahedron (triangular pyramid) with an edge length of four eggs. Unfortunately, both egg-sacs fell apart in the collecting jar, making exact egg counts impossible. However, the tetrahedral shape seems to predict a relatively constant number of 20 eggs [Tn = n (n +1)(n +2)/6]. For the spider, this egg-sac shape may result from a simple sphere packing problem (i.e. the problem to find an arrangement in which the spheres fill as large a proportion of the space as possible). The proportion of space filled by the spheres is called the density of the arrangement, and a face-centred cubic packing as in a tetrahedron fills a maximum of ∼74% of space ( Hales 2000). However, face-centred cubic packing need not necessarily result in a tetrahedron, so the biological reason for the tetrahedron remains largely unclear.
Apparently widely distributed in West African rainforests ( Figure 148 View Figures 148–149 ).
GUINEA: Guinée Forestière : Forêt Classée de Diéké (7°32.0′N, 8°49.9′W), 430 m above sea level (a.s.l.), 1.xii.2008 (B.A. Huber), 236♀ in ZFMK GoogleMaps ; same data, 131♀ 3 juv. in pure ethanol, in ZFMK GoogleMaps ; Forêt Classée de Ziama (8°24.2′N, 9°19.3′W), 640 m a.s.l., 2.xii.2008 (B.A. Huber), 436♀ in ZFMK GoogleMaps ; same data, 3♀ 1 juv. in pure ethanol, in ZFMK GoogleMaps ; Mount Nimba (∼ 7°41.5′N, 8°24.5′W), ∼ 600 m a.s.l., forest, 29.xi.2008 (B.A. Huber), 3♀ in ZFMK GoogleMaps ; same data, 2♀ 3 juv. in pure ethanol, in ZFMK GoogleMaps .
CÔTE D’IVOIRE: Apouesso, FC Bossematié (6°35′N, 3°28′W), rain forest, station 1, glue trap, 12.-13.xi.1995 ( R. Jocqué), 23 in MRAC GoogleMaps (202553).
GHANA: Kakum forest (5°20′N, 1°23′W), secondary forest GoogleMaps , 15.xi.2005 ( R. Jocqué , D. de Bakker, L. Baert), “fog 4”, 33 in MRAC (217697) ; same data but primary forest , 21.xi.2005, “fog 9”, 5♀ in MRAC (217733) ; 18.xi.2005, “fog 7”, 1♀ in MRAC (217728) ; 23.xi.2005, “fog 11”, 1♀ in MRAC (217684) ; 25.xi.2005, “fog 13”, 3♀ in MRAC (217717).
CAMEROON: South Region: near Kribi (2°54.0′N, 9°54.4′E), 20 m a.s.l., 9.iv.2009 (B.A. Huber), 434♀ in ZFMK GoogleMaps ; same data, 5♀ 4 juvs. in pure ethanol, in ZFMK GoogleMaps . Between Kribi and Campo , “site 1” (2°42.2′N, 9°51.8′E), 10 m a.s.l., 10.iv.2009 (B.A. Huber), 1♀ in pure ethanol, in ZFMK GoogleMaps . Near Ebolowa (2°54.9′N, 11°08.3′E), 620 m a.s.l., 11.-12.iv.2009 (B.A. Huber), 2♀ in ZFMK GoogleMaps ; same data, 2♀ 2 juvs. in pure ethanol, in ZFMK GoogleMaps . North of Mengong (3°03.0′N, 11°25.0′E), 690 m a.s.l., 13.iv.2009 (B.A. and J.C. Huber), 1♀ in pure ethanol, in ZFMK GoogleMaps . Littoral Region: near Loum , forest with banana plants (4°43.6′N, 9°42.5′E), 400 m a.s.l., 24.iv.2009 (B.A. and J.C. Huber), 43 4♀ in ZFMK GoogleMaps ; same data, 2♀ 2 juvs. in pure ethanol, in ZFMK GoogleMaps . Near Edéa, Koukoué (3°41.2′N, 10°06.4′E), 50 m a.s.l., 8.iv.2009 (B.A. Huber), 1♀ in pure ethanol, in ZFMK GoogleMaps .
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