Figure 1.
Schematic illustration of a distal spider tarsus bearing scopula and claw tuft.
The adhesive setae are coloured in dark grey. In a living specimen they usually appear dark, with the lamellate part being translucent and with an iridescent lustre on the adhesive side.
Figure 2.
Characters of setal types occurring in the distal tarsus/claw tuft.
For detailed description see [25]. AS, adhesive seta (with spatulae); FS, frictional seta (without spatulae); SB, serrated bristle (see [55]).
Figure 3.
Evolution of hairy adhesive pads and web loss in spiders.
A. Phylogenetic relationships among the Araneae, adapted from the most recent literature survey (see [30] for details), and the distribution of adhesive (spatulae-bearing) setal pads and web abandoning. Character traces follow the Ancestral State Reconstruction performed with the Mesquite software. B. Combined character traces of pad type distribution in the RTA-clade. The model clearly suggests an early origin of scopulae and the derived state of claw tufts.
Figure 4.
Electron microscopy of isolated setae, different scales.
A. SEM micrographs of distal tips of claw tuft setae, rear view. Arrowheads indicate the remaining tapered tip of the expanded setae. a. Adhesive seta type IIb in Micaria formicaria (Gnaphosidae). b. Adhesive seta type III in Clubiona pallidula (Clubionidae). c. Large adhesive seta type IIa in Anyphaena accentuata (Anyphaenidae). B. SEM micrographs of setae, lateral view. Arrowheads indicate the twisted lamella shaft occurring in claw tuft setae. d. Frictional seta type II in Xysticus lanio (Thomisidae) ventral tarsus. e. Scopula seta of type IIb in Clubiona lutescens (Clubionidae) prolateral tarsus. f. Scopula seta of type IIb in Palpimanus gibbulus (Palpimanidae) prolateral metatarsus. g. Brush like claw tuft seta of type Ia in Homalonychus selenopoides (Homalonychidae), a presumably primitive character. h. Claw tuft seta of type IIb in Euophrys frontalis (Salticidae). i. Claw tuft seta of type III in Clubiona pallidula. k. Claw tuft seta of type IIa in Anyphaena accentuata. C. TEM micrographs of sections of the distal part of tarsal setae. l. Frictional seta type II in Nops largus (Caponiidae). m. Adhesive seta type Ia in Xysticus cristatus (Thomisidae). n. Adhesive seta type IIb in Evarcha arcuata (Salticidae). o. Adhesive seta type IIa in Anyphaena accentuata.
Figure 5.
Body size and preferred microhabitat.
Box plots showing the 25th and 75th percentiles and the median line; error bars define the 1.5 times interquartile range; rest values are marked by single circles. Numbers at the bottom give the species numbers sampled (each including the mean width of ten randomly chosen setae/spatulae of the distal part of the claw tuft). Seta width differs significantly between species of different families (Kruskal-Wallis rank sum test: p = 0.000), but not between differently sized (p = 0.155) and ecological groups (p = 0.102) of the overall sample. The same holds for spatula size (families: p = 0.030; size = 0.377; microhabitat = 0.860).
Figure 6.
Distribution of adhesive setae in spiders.
Above: proportions of species bearing claw tufts, scopulae (incl. ‘false’ claw tufts), both or none, combined with lifestyle. Tree and plots below indicate proportions among the different lineages, with sizes of first plots resembling the number of species (numbers given in italic font). Results show the two major evolutionary pathways of spiders, web builders and free hunters, out of which the latter ones are often associated with adhesive setae.
Figure 7.
SEM micrographs of the distal portion of spider tarsi bearing the tarsal claws and setal pads; ventral or prolateral view; scale bar - 50 µm.
A. Primitive pretarsus in the ancient Heptathela sp. (Liphistiidae), juvenile, lacking specialized setae. B. Distal tarsus of Malthonica ferruginea (Agelenidae) with a dense ventral coverage of FS-II setae typically occurring in spiders of the basic web types. C. Distal tarsus of the desert dwelling Sicarius sp. (Sicariidae), with reduced setal structures. D. Distal tarsus of Trabea paradoxa (Lycosidae), showing distally extended scopula, resulting in a primitive foot pad (‘false’ claw tuft). E. Distal tarsus of Drassodes lapidosus (Gnaphosidae), with an extended scopula, including a ‘false’ claw tuft. Note the seta width increasing in the distal part of the pad. F. Derived prey capture leg in Palpimanus gibbulus (Palpimanidae), bearing the scopula with spatulate setae. G. Distal tarsus of Clubiona terrestris (Clubionidae) featuring both scopulae and claw tufts. Note the foot pad emerging from the pretarsus, thus being retracted together with the claws. H. Distal tarsus of Marpissa muscosa (Salticidae), bearing only the restricted claw tufts. I. Distal tarsus of the sand-dwelling desert spider Homalonychus selenopoides (Homalonychidae), bearing claw tufts with brush-like, non-widened adhesive setae. K. Distal tarsus of Misumena vatia (Thomisidae), lacking adhesive setae, a presumed secondary loss. L. Distal tarsus of Araneus quadratus (Araneidae), bearing the serrated bristles and the enlarged third claw, adaptations of the derived web building taxa. M. Distal tarsus of the web building Fecenia cylindrata (Psechridae), including claw tufts, a great exception in silk trappers.
Figure 8.
Cryo-SEM micrograph of male Euophrys frontalis (Salticidae) pretarsus, showing mechanics of claw tuft spreading.
A. Pretarsus with the claw tuft retracted (low hemolymph pressure). B. Claw tuft protracted under high hemolymph pressure, caused by tight squeezing of the femur. Deformation causes a spreading of the divided claw tuft und protraction of the claws, probably important for fast detachment.