CUTICULAR SCALES OF SPIDERS

Because the morphology of the cuticular scales of spiders is extremely variable both within and between families,anny study attempting to use cuticular scales as a systematic character must first have a formal definition that differentiates scales from other types of setae. The purpose of our study was to evaluate the characters used previously in the literature to distinguish cuticular scales from other types of setae and, if necessary, to provide a new, comprehensive definition for this setal type in spiders. The results of our SEM survey of the surface morphology of the scales of 23 species of spiders representing 10 families do not support the morphology of the socket as a reliable character for distinguishing scales from other types of setae. Our results indicate that cuticular scales should be defined as flattened setae that have a pedicel bent so that the scale overlays the surface of the cuticle. Our results also suggest that the urticating hairs of theraphosid spiders should not be considered to be a type of cuticular scale. Instead, we propose the recognition of three main types of scales: lanceolate, spatulate, and plumose. In addition to qualitative comparisons, we measured and compared the cuticular scales for several species and found that differences in scale width were directly related to the morphotype of the scales being examined. Additional key words: Araneae, morphology, SEM, macrosetae, urticating hairs Of the 105 currently recognized families of spiders (Coddington & Levi 1991), 13 families have at least one species that possesses cuticular scales (Kaston 1978; Roth 1993; Townsend, unpubl. data). These families are the Anyphaenidae, Araneidae, Corinnidae, Gnaphosidae, Heteropodidae, Liocranidae, Lycosidae, Oxyopidae, Philodromidae, Pisauridae, Salticidae, Thomisidae, and Uloboridae. Thus far, the microanatomy of the cuticular scales of spiders has been described adequately only for the Salticidae (Galiano 1975; Wanless 1978a, b; Hill 1979; Cutler 1981, 1987; Cutler & Jennings 1985; Felgenhauer 1998) and the Oxyopidae (Lehtinen 1975; Townsend & Felgenhauer 1998a). In these spiders, cuticular scales exhibit a tremendous diversity of colors, distributional patterns, and morphology. In certain species, scale morphology, distributions, and colors have even been observed to vary ontogenetically (Crane 1948; Townsend & Felgenhauer 1998a, b) and sexually (Kaston 1978; Hill 1979; Townsend & Felgenhauer 1998a). At least two definitions for the cuticular scales of spiders exist in the published literature (Hill 1979; Roth 1993). According to Roth (1993), cuticular scales a Author for correspondence. E-mail: vrt5719@usl.edu are flattened setae that lack innervation and have a highly reduced socket morphology; Roth (1993) also recognized the three major morphotypes of the scales of spiders as being lanceolate, spatulate, and lamelliform. In his definition, Roth (1993) considered the urticating hairs of theraphosid spiders (i.e., tarantulas) to be a type of cuticular scale. Urticating hairs are setae that lack innervation, occur in four distinct morphotypes (Types I-IV), and typically exhibit a localized distribution, i.e., a single dense patch of hairs on the dorsal surface of the opisthosoma (Cooke et al. 1972). In contrast to Roth's definition, Hill (1979) defined a cuticular scale as being a modified, flattened seta composed of fused cuticular elements that has a pedicel bent at an obtuse angle so that the scale overlays the surface of the cuticle. In his discussion of cuticular scales in spiders, Hill (1979) made no reference to socket morphology, innervation, or homologies with the urticating hairs of tarantulas. Terminology used to describe the specific features of the surface morphology of cuticular scales of spiders was adopted by Hill (1979) from the terminology used to describe the surface features of the cuticular scales of lepidopteran insects (Downey & Allyn 1975). For instance, the proximal tip of the scale that inserts into the socket is known as the pedicel (Fig. 1). In This content downloaded from 157.55. 39.163 on Wed, 21 Sep 2016 05:58:03 UTC All use subject to http://about.jstor. org/terms Cuticular scales of spiders ~~~~~~oMPw11wb-;O"a _16 *--# Figs. 1-4. SEM micrographs of the major surface features of the cuticular scales of spiders. Fig. 1. The dorsal surface of the opisthosoma of the salticid spider, Phidippus audax. Note the bent pedicel (p) of a scale. Scale bar, 30 pm. Fig. 2. Inferior surface of the cuticular scales from the prosoma of the salticid spider, Hentzia mitrata. Inferior spine (is). Scale bar, 10 pm. Fig. 3. The dorsal surface of the prosoma of the oxyopid spider, Oxyopes salticus. Note plicae (pl) occurring on the superior surface of a scale. Scale bar, 15 wLm. Fig. 4. The prosoma of the anyphaenid spider, Aysha velox. Note setule (sl) originating from the lateral surface of a scale. Scale bar, 20 lim. jumping spiders, the pedicel is bent so that an -135? angle is formed between the pedicel and the blade of the scale (Hill 1979). Small projections occurring on the lateral, inferior, and superior surfaces, as well as at or near the tip, are termed spines and are named on the basis of their location. For example, projections occurring near the tip are known as apical spines, whereas those occurring on the inferior surface are known as inferior spines (Fig. 2). Ridges, in turn, that are arranged in a longitudinal orientation along the long axis of the scale are called shafts, whereas smaller, lateral ridges are termed plicae (Fig. 3). Small lines or depressions on the superior or inferior surfaces are known as striae, while long, relatively thin processes that arise from the lateral surfaces are called setules (Fig. 4). In contrast to the paucity of research devoted to the cuticular scales of spiders, the morphology and ultrastructure of the scales of lepidopteran insects have been examined in many studies (Snodgrass 1935; Overton 1966; Chapman 1969; Greenstein 1972; Ghiradella 1974, 1984, 1985, 1989, 1994; Nijhout 1980). In these insects, cuticular scales have been observed to serve multiple functions (Scoble 1995) including defense (Robinson et al. 1969), thermoregulation (Chapman 1969), and communication (Birch et al. 1990). In spiders, scales have been hypothesized to function in similar capacities (Simon 1901-1903; Hill 1979; Cutler 1987), but no empirical research has been published that has experimentally tested any of these proposed functions. The general purpose of our study was to examine and evaluate the morphological characteristics of cuticular scales that were proposed originally by Hill (1979) and Roth (1993) and, by doing so, provide a comprehensive definition for cuticular scales in spiders. In addition, through a comparison of the surface morphology of cuticular scales and urticating hairs, we sought to clarify the relationship between these two distinct types of setae. To accomplish these tasks, a 319