Comparative Morphology and Functional Significance of Setae Called Papillae on the Pedipalps of Male Camel Spiders (Arachnida: Solifugae)

Abstract

Some male camel spiders (Arachnida: Solifugae) in the families Eremobatidae, Karschiidae, and Solpugidae have clusters of specialized conical or acuminate setae called papillae, on the ventral surface of the metatarsus of the pedipalps. We compared the overall structure of the papillae found on representatives of the three families using scanning electron microscopy (SEM). We examined the ultrastructure of these setae using transmission electron microscopy (TEM). We also used extracellular electrophysiological recording techniques to examine the electrical properties of these sensory structures and test the hypotheses that they function as mechanoreceptors, olfactory receptors, and chemoreceptors.Wefound similarities in the structure of papillae among genera within a family or distinct family-level differences in structure. Thus, the papillae are phylogenetically informative; similar within family but differing between families. TEM results demonstrated the cuticular wall of a papilla is divided into three sublayers: endo-, meso-, and exocuticle. Mechanoreceptive dendrites are evident at the base of the setal shaft. Other dendrites innervate the shaft of the papilla and penetrate through the cuticular layers near the setal apex. Two SEM images show what appear to be pores on the branches of the papillae, and we found what appears to be a pore tubule extending from the distal portion of the dendrites through the exocuticular layer. Electrophysiological data support the hypothesis that the papillae function as mechanoreceptors and provide no support for chemosensory, thermoregulatory, or hygroreceptive functions. Our data suggest that the papillae function as mechanoreceptors and may also function as chemoreceptors.

Cheliceral Morphology in Solifugae (Arachnida): Primary Homology, Terminology, and Character Survey

“…For example, Snodgrass (1948) proposed new terminology for the mouthparts of Acari, based on careful investigations of mouthpart homology across arachnids (including terms recently promoted for the Solifugae rostrum; see , which was largely ignored by acarologists, because a relatively standardized terminology was already in place. Given the inconsistency in solifuge morphological terminology, and the renewed interest in solifuge research (e.g., Ballesteros and Francke, 2007;Catenazzi et al, 2009;Klann, 2009;Carvalho et al, 2010;Erdek, 2010;Reddick et al, 2010;Bayram et al, 2011;Cushing and Castro, 2012;Dunlop et al, 2012;González Reyes and Corronca, 2013;Karataş and Uçak, 2013;Cushing et al, 2014;Botero-Trujillo, 2014;Iuri et al, 2014, Wharton andReddick, 2014), it is an opportune time to unify and redefine solifuge morphological terminology in light of modern concepts of character homology, advances in technology, and the availability of new material.…”

Mechanosensory pathways of scorpion pecten hair sensillae—Adjustment of body height and pecten position

“…Arachnids evolved diverse, and often unique, sensory structures on varying body parts to explore their surroundings regarding chemo-and mechanosensory information and to establish adequate response profiles. Examples for such sensory organs are the antenniform legs of Thelyphonida (e.g., Haupt, 1996;Moro & Geethabali, 1985;Sinakevitch et al, 2021) and Amblypygi (e.g., Foelix & Hebets, 2001;Santer & Hebets, 2011;Segovia et al, 2020), the leglike pedipalps of Solifugae (e.g., Cushing & Casto, 2012;Cushing et al, 2014), the pedipalps of Aranea (e.g., Barth, 2002b;Foelix, 1996;Ganske & Uhl, 2018), or the sensory legs I and II in Opiliones (e.g., Bishop, 1949;Elpino-Campos et al, 2001;Hillyard & Sankey, 1989;Hoenen & Gnaspini, 1999;Willemart & Chelini, 2007;Willemart et al, 2009).…”

“…Arachnids evolved diverse, and often unique, sensory structures on varying body parts to explore their surroundings regarding chemo‐ and mechanosensory information and to establish adequate response profiles. Examples for such sensory organs are the antenniform legs of Thelyphonida (e.g., Haupt, 1996; Moro & Geethabali, 1985; Sinakevitch et al., 2021) and Amblypygi (e.g., Foelix & Hebets, 2001; Foelix et al., 1975; Santer & Hebets, 2011; Segovia et al., 2020), the leg‐like pedipalps of Solifugae (e.g., Cushing & Casto, 2012; Cushing et al., 2014), the pedipalps of Aranea (e.g., Barth, 2002b; Foelix, 1996; Ganske & Uhl, 2018), or the sensory legs I and II in Opiliones (e.g., Bishop, 1949; Elpino‐Campos et al., 2001; Hillyard & Sankey, 1989; Hoenen & Gnaspini, 1999; Willemart & Chelini, 2007; Willemart et al., 2009). Intriguingly, scorpions did not convert walking leg pairs into distinct sensory appendages, but evolved comb‐like appendages on the ventral side, posterior to the walking legs (the so‐called pectines) that probe the substrate regarding chemo‐ and mechanosensory information (e.g., Brownell & Farley, 1979a,b; Drozd et al., 2020; Foelix & Schabronath, 1983; Hoffmann, 1965; Hughes & Gaffin, 2019; Kladt et al., 2007; Vachon, 1973; Wolf, 2008, 2016, 2017).…”

A preliminary study on fauna of medical important solpugid (Chelicerata: Arachnida: Solifugae) in Kashan City, Central Iran.

“…The pedipalps of these animals have different papillae and hairs that are various in different families. They play a basic role as mechanical and chemical receptors [18,19]. Solpugids have so powerful Chelicerae that they can easily hunt preys larger than themselves.…”