2012. The Journal ofArachnology 40:123-127 SHORT COMMUNICATION Preliminary survey of the setal and sensory structures on the pedipalps of camel spiders (Arachnida: Solifugae) Paula E. Cushing and Patrick Casto: Denver Museum of Nature & Science, Department of Zoology, 2001 Colorado Blvd., Denver, Colorado 80205, USA. E-mail: [email protected] Abstract. Solifuges, or camel spiders (order Solifugae), keep their pedipalps extended when moving through the environment, utilizing them much the way insects use their antennae. The male also uses his pedipalps during copulation, staying in contact with the female throughout the process. The pedipalps are covered with setae that are assumed to function as chemo-, mechano-, thermo-, hygro-, and olfactory receptors. We surveyed setal forms and other possible sensorystructuresonthepedipalps ofsolifugestodetermine 1) ifcertain setaeand structuresarecommon to all families, 2) ifsomemay be unique tocertain families, and 3) the possible function ofthevarious setae and other structures. Wefound that all families had bifurcated and tapered setae, and that all families had dorsal tarsal pores. Other setal forms were evident only in one or a few families. Three of the setal types had distal pores suggesting that they function as chemoreceptors. These data suggest that the pattern and types of setae on the pedipalps of solifuges may be phylogenetically informative and confirm that the pedipalps do function as sensory appendages. Keywords: Chemoreceptor, mechanoreceptor, sensory receptor, Blumenthal organ, tarsal organ Arachnologists have studied solifuges for decades, yet solifuge objectiveofthisstudywastocarryoutapreliminarysurveyofthesetae biology is still elusive (Punzo 1998). In particular, only a few studies and other possible sensory structures found on the pedipalps of 12 have been carried out to elucidate the functional significance of species representingeach ofthe !2 families in the order. morphological structures unique to these arachnids (Bertkau 1892; WeusedScanningElectron Microscopy(SEM)toexaminethesetal Roewer 1934; Junqua 1966; Brownell & Farley 1974; Haupt 1982; morphology of the pedipalps of solifuges that represent the 12 Bauchhenss 1983; Cushinget al. 2005; Klann et al. 2005, 2008; Klann families of the order (Table 1). We used a FEI Quanta 450 Field & Alberti 2010). Emission Gun at the U.S. Geological Service (USGS) Denver The pedipalps, in particular, are in need of morphological study. Microbeam Laboratory. To prepare each specimen, we cut off the Solifuges keep their pedipalps anteriorly extended when moving right pedipalpat thecoxus,washed offanyobviousdirt with absolute through the environment (Punzo 1998). They utilize them during ethanol and sonicated the pedipalp in absolute ethanol for 30- hunting,astheyhavesuctorialorganstohelpbringpreyclosertotheir 45 seconds. We then allowed thepedipalpto airdry beforeexamining chelicerae (Cushing et al. 2005; Klann et al. 2008; Willemart et al. it under the light microscope to make sure visible impurities were 2011). Malesalsousetheirpedipalpsduringmating, stayingincontact minimal. Depending on the size of the pedipalp, we either mounted with thefemales through theentire process, suggesting that there may the pedipalp on a 12.5 mm diameter aluminum stub or on a glass be structures on the pedipalps functioning in intraspecific communi- slide. The pedipalps were mounted with double-sided sticky carbon cation. Haupt (1982) looked at the morphology ofchemotactile setae tape. We used the USGS Microbeam Labprotocol togold sputterthe on the second and third legs of solifuges, and Bauchhenss (1983) stubs for 35-45 seconds and then placed them into the SEM for examinedthemorphologyand ultrastructureofsensillaampullaceaon examination. We photographed an entire view ofeach segment ofthe the pedipalps. Beyond these studies and those on the suctorial organ pedipalp in order to pinpoint setae of interest (Fig. 1A). We then (Cushingetal.2005; Klannetal. 2008), littleotherworkhasbeendone magnified and photographed individual setae (Fig. IB). Next, we on the sensory structures found on the appendages ofsolifuges. The focused on the tip and the base ofeach unique seta (Figs. 1C, ID). Table 1.—Specimens used for SEM analysis. AMNH = American Museum of Natural History, CAS = California Academy of Sciences, DMNS = Denver Museum ofNature and Science, SMN = National Museum ofNamibia. Stub # Specimen # Family Species Ami DMNS ZA.23498 Ammotrechidae Branchia angustus Muma 1951 Cel SMN 13632 Ceromidae Ceroma inerme Purcell 1899 Dal SMN 13278 Daesiidae Biton browni (Lawrence 1965) Erl DMNS ZA.22647 Eremobatidae Eremohatespallipes (Say 1823) AMNH GGyall SMN 134663224 GGyalliepopdiiddaaee GTarliecohdoetsomoalivmiiecrhiaSelismeonni (1K8r7a9epelin 1914) AMNH Hel 5768 Hexisopodidae Chelypus barberi Purcell 1902 AMNH Kal 10687 Karschiidae Karschia mastigofera Birula 890 Mel AMNH 10737 Melanoblossidae Melanoblossia braunsi Purcell1 1903 Mul CAS 9033889 Mummuciidae Mummucia sp. AMNH Rhl 2293 Rhagodidae Rhugodes melanus (Olivier 1807) AMNH Sol 7569 Solpugidae Zeria sericeci (Pocock 1897) 123 124 THE JOURNAL OF ARACHNOLOGY (Lawrence 1965)] seem to have unique setae (Figs. 2F, H, I). The nozzle tipseta (Fig. 2F), onetypeoftruncatedtipseta(Fig. 2M), and thetapered tipseta(Fig. 2K)all haveterminal pores; thus, wesuspect these function as chemoreceptors. Arthropod chemoreceptors can generally be distinguished byan apical pore (Slifer 1970; Foelix 1970; Foelix & Chu-Wang 1972; Harris & Mill 1973; Zacharuk 1980; Barth 2001; Talarico et al. 2006). The other setal types lack pores and may function as mechanoreceptors or as other types ofsensory receptors (e.g., hygroreceptors, thermoreceptors, proprioreceptors). Theotherstructuresfound on thesurfaceofthepedipalpsmayhave some phylogenetic importance. Hexisopodidae Chelypus barberi ( Purcell 1902) was the only family with spines on the tarsus, although additional species from the variousfamiliesmust beexamined. Dorsal tarsal pores were seen in all 12 species representing the 12 families (Figs. 3A-D). These structures have been previously described (Bertkau 1892; Bauchhenss 1983). They occur in fields, containing a fewtodozensofporeswithinafieldalongthedorsalsurfaceofthetarsi (Figs. 3A, C). The shape of these fields may be phylogenetically informative; e.g., in Galeodes olivieri (Galeodidae), the field ofpores extends diagonally from the proximo-medial surface of the tarsus, across the dorsal surface, ending at the anterio-latera! surface ofthe segment (Bauchhenss 1983 and Fig. 3A), whereas in C. barberi the Figure 1. Pedipalp segments and structures that were photo- pores are in two parallel groups down the dorsal surface ofthe tarsus graphed. A) Tarsal segment of Rhagodes melanus (Rhagodidae), B) (Fig. 3C).TherewerefewertarsalporesonthepedipalpsofMummucia seta on femur ofTricholomamichaelseni(Gylippidae), C) base ofseta sp. (Mummuciidae) and Melanoblossia braunsi Purcell 1903 (Melano- on metatarsus of EremobatespaUipes (Eremobatidae), D) tip ofseta blossidae). Bauchhenss (1983) suggested that reduction in the number on metatarsus of Ceroma inerme (Ceromidae). Scale line A = 3 mm, ofporesmaybeanadaptationagainstwaterlossthroughevaporation, scale line B = 50 pm, scale lines C & D = 2 pm. although this hypothesis will have to be tested. These pores are hypothesized to be homologous to Blumenthal’s tarsal organs in Araneae, which are hypothesized to function as olfactory organs We found 13 distinguishable setal types, mostly defined by the (Bauchhenss 1983; Foelix 201 1). Metatarsalpitswereveryapparenton shape of the shaft and tip (Figs. 2A M, Table 2). All sensory setae the pedipalps of C. barberi (Figs. 3E-F); however, further analysis is emerged from morphologically similar sunken pits. Thus, we mostly required to determine the possible function of these structures. The show only the tips and parts of the shafts of the different setae in concave shapes ofthe pits are noticeable enough to suggest that they Fig. 2. Table 2 summarizes how common each type ofseta is among may be ofsensory importance. The pits are distributed evenly around the 12 families. The bifurcated seta (Fig. 2A) and tapered tip seta the surface ofthe metatarsus (Fig. 3E). (Fig. 2K) are common to all families. Some families such as This preliminary study of the sensory setae and structures on the Ceromidae (Ceroma inerme Purcell 1899) and Daesiidae [Bitonbrowni pedipalps ofSolifugae has revealed structures common to all families Table 2.—Distribution ofsetae among the twelve families. Setal Ammo- Cero- Dues- Eremo- Gale- Gylip- Hexiso- Karsch- Melano- Mumrnuc- Rhagod- Solpug- types trechidae midae iidae batidae odidae pidae podidae iidae blossidae iidae idae idae Bifurcated X X X X X X X X X X X X Blunt X X X X X X X X X Cavitate baton X Clubbed X X X X Imbricate X X X X X X X X Nozzle X Papillae X X X Polymicro- digitus annulus X Polymicro- digitus imbricate X Simple X X Tapered X X X X X X X X X X X X Truncated X X X X X X X X Truncated with pore X X Metatarsal pits Tarsal pores X X X X X X X X X X X X CUSHING & CASTO—SETAL AND SENSORY STRUCTURES OF SOLIFUGES 125 — Figure 2. Setaltypesfound on thepedipalpsofsolifuges. A) Bifurcatedseta tipon tarsusofCeromainerme(Ceromidae), B) blunt seta tipon the tibia ofTrichotomamichaelseni(Gylippidae), C) cavitate baton seta on metatarsus on Galeodesolivieri(Galeodidae), D) clubbed seta tip on tarsusofEremobatespallipes(Eremobatidae), E)imbricatesetatipon tibia ofC. inerme F) nozzleseta tipon femurofC. inerme(arrowpointsto , pore), G) papilla on metatarsus of E. pallipes, H) polymicrodigitus (annulus) seta tip on femur of Biton browni (Daesiidae), I) polymicrodigitus (imbricate) seta tip on femur of B. browni, J) simple seta tip on fMemur of E. pallipes, K) tapered seta tip on tarsus of B. b(rAomwmnoit,reLc)hitdrauenc)at(eadrrosewtapoitinptsotno ptoarres)u.s Aolfl sTc.almeiclihnaeesls=en2i pwimthexcneoptpoGre=e5vi0depnmt., ) truncated seta tip on tarsus of Bronchia angustus 126 THE JOURNAL OF ARACHNOLOGY — Figure 3. Otherstructures found on the pedipalps ofsolifuges. A) Dorsal tarsal pore Field ofGaleodesolivieri(Galeodidae) (arrows pointto pores), B) single dorsal tarsal pore of G. olivieri, C) tarsus with parallel dorsal tarsal pore fields of Chelypus barberi (Hexisopodidae) (arrows point to pore Fields), D) dorsal tarsal poreField ofC. barberi, E)distribution ofmetatarsal pitsofC. barberi(arrows point topits), F)metatarsal pit of C. barberi. Scale lines B & F = 2 pm; scale lines A, E, & D = 50 pm; scale line C = 100 pm. suchasthedorsal tarsalpores. Wehavealsoidentified setaecommonto Brownell, P.H. & R.D. Farley. 1974. The organization of the all families and setae that may be unique to individual families. malleolar sensory system in the solpugid, Chanbria sp. Tissue Additional taxa within each ofthe 12 families must beexamined in the and Cell 6:471-485. future to verify the apparent phylogenetic usefulness of these sensory Cushing, P.E., J.O. Brookhart, H-J. Kleebe, G. Zito & P. Payne. structures.Inaddition,inordertodeterminethefunctionofthedifferent 2005. The suctorial organ ofthe Solifugae (Arachnida, Solifugae). types ofsetae, three experiments should be performed: 1) electrophys- Arthropod Structure and Development 34:397-406. iology to detect mechano-, chemo-, hygro-, thermo-, and olfactory Foelix, R.F. 1970. Structure and function of tarsal sensilla in the reception; 2) histological analysis to map out dendritic placement and spider Araneus diadematus. Journal of Experimental Zoology helpconfirmfunction;and3)behavioralstudiestoanalyzesetalfunction 175:99-124. in their environment. Nevertheless, the present study verifies that the Foelix, R.F.&I-W.Chu-Wang. 1972. Finestructuralanalysisofpalpal pedipalps ofsolifugesdo playa major role in sensory perception. receptors in the tick Amblyomma americanum (L.). Zeitschrift fur ACKNOWLEDGMENTS Zellforschung und Mikroskopische Anatomic 129:548-560. Foelix, R.F. 2011. Biology of Spiders. Third edition. Oxford Thanks to USGS and Heather Lowers for the use of their SEM. University Press, New York. Thanks to Lorenzo Prendini (AMNH), Charles Griswold (CAS), and Harris, D.J. & P.J. Mill. 1973. The ultrastructure of chemoreceptor Tharina Bird (SMN) for the loan and use ofspecimens. Thanks also sensilla in Ciniflo(Araneidae, Arachnida). Tissueand Cell 5:679-689. to two anonymous reviewers for their helpful comments. This study Haupt, J. 1982. Hair regeneration in a solifugid chemotactile was supported by National Science Foundation grants DEB-0346378 sensillum during molting (Arachnida: Solifugae). Wilhelm Roux’s and DEB-1112263 awarded to Paula E. Cushing and DEB-0228699 Archives 191:137-142. awarded to Lorenzo Prendini. Junqua, C. 1966. Recherches biologiques et histo-physiologiques sur un solifuge saharien Olhoes saharae Panouse. Memoires du LITERATURE CITED Museum National d’Histoire Naturelle Paris, n.s. 43:1-124. Barth, F.G. 2001. A Spider’s World: Senses and Behavior. Springer- Klann, A.E. & G. Alberti. 2010. Histological and ultrastructural Verlag, Berlin. characterization ofthe alimentary system ofsolifuges (Arachnida, Bauchhenss, E. 1983. Morphology and ultrastructure of sensilla Solifugae). Journal ofMorphology 271:225-243. ampullacea in Solifugae (Chelicerata: Arachnida). International Klann, A.E., A.V. Gromov, P.E. Cushing, A.V. Peretti & G. Alberti. Journal of Insect Morphology and Embryology 12:129-138. 2008. The anatomy and ultrastructure of the suctorial organ of Bertkau, P. 1892. Uber Sinnesorgane in den Tastern und dem ersen Solifugae (Arachnida). Arthropod Structure and Development Beinpaar der Solpugiden. Zoologische Anzweiger 15:10-13. 37:3-12. CUSHING & CASTO—SETAL AND SENSORY STRUCTURES OF SOLIFUGES 127 Klann, A.E., A.V. Peretti & G. Alberti. 2005. Ultrastructure ofmale Talarico, G., J.G. Palacios-Vargas, M. Fuentes Silva & G. Alberti. genital system and spermatozoa ofa Mexican camel-spider ofthe 2006. Ultrastructure of tarsal sensilla and other integument Eremobatespallipes species group (Arachnida, Solifugae). Journal structures of two Pseudocellus species (Ricinulei, Arachnida). ofArachnology 33:613-621. Journal ofMorphology 267:1063-1065. Punzo, F. 1998. The Biology of Camel-Spiders (Arachnida, Solifu- Willemart, R.H., R.D. Santer, A.J. Spence & E.A. Hebets. 2011. A gae). Kluwer Academic Publishers, Boston. sticky situation: solifugids (Arachnida, Solifugae) use adhesive Roewer, C.F. 1934. Solifugae, Palpigradi. Pp. 161^)80. In Klassen organs on their pedipalps for prey capture. Journal of Ethology und Ordungen des Tierreichs. 5: Arthropoda. IV Arachnoidea, 29:177-180. vol. 3-5 (H.G. Bronn, ed.). Akademische Verlagsgeseilschaft Zacharuk, R.Y. 1980. Ultrastructure and function of insect chemo- Leipzig. sensilla. Annual Review ofEntomology 25:27-47. Slifer, E.H. 1970. Thestructureofarthropodchemoreceptors. Annual Review ofEntomology 15:121-142. Manuscript received30 August 2011, revised11 January2012.