Interspecific variation in the microanatomy of cosmetid harvestmen (Arachnida, Opiliones, Laniatores)

Abstract

Scanning electron microscopy (SEM) is a useful tool for identifying interspecific variation in often overlooked structures that may represent useful sources for informative phylogenetic characters. In this study, we used SEM to compare the morphology of 12 cosmetid species from Central America, the Caribbean, and North America including multiple species for the genera Cynorta, Erginulus, and Paecilaema. To determine if microanatomical structures were unique to the cosmetid taxa under examination, we investigated the microanatomical structures of six additional species of gonyleptoidean harvestmen representing the families Agoristenidae, Cranaidae, Gonyleptidae, Manaosbiidae, and Stygnidae. Our results indicate that the shape of the ocularium (narrow, intermediate, or broad) did not vary within cosmetid genera, whereas the morphology of the rough pit glands on the eye mound varied considerably between species. Each cosmetid species had 10-20 rough pit glands on the ocularium whereas only the eye mounds of Avima intermedia (Agoristenidae) and Glysterus sp. (Gonyleptidae) had similar structures. With regards to the surface texture of the dorsal scutum, cosmetid harvestmen exhibited a rivulose-microgranulate morphology (6 species), a microtuberculate-rivulose-microrgranulate morphology (4 species), or a microgranulate morphology (2 species). In contrast, each of the gonyleptoidean species exhibited a microgranulate pattern, with the exception of Stygnoplus clavotibialis, which had a rivulose-microgranulate surface texture. For cosmetid harvestmen, we observed considerable interspecific variation in the shape and number of teeth on the fixed and moveable fingers of the male chelicerae. Similarly, we also observed interspecific variation in the distribution and shape of tubercles on the ventral and dorsal surfaces of the femur of the pedipalp. Overall, our results indicate that there are several microanatomical structures associated with the ocularium, dorsal scutum, male chelicera, and pedipalp that could represent informative phylogenetic characters in future taxonomic studies of cosmetid harvestmen.

Survey of cuticular structures on leg IV of cosmetid harvestmen (Opiliones: Laniatores: Gonyleptoidea)

“…They exhibited interspecific variation with respect to occurring on the surface of the cuticle and in the prominence of the pores (Table 2). Rodriguez et al (2014) found rough pit glands to be common on the ocularium and anterior region of the dorsal scutum in these same species of cosmetid harvestmen, but absent from other gonyleptoidean harvestmen, with the notable exceptions of agoristenid and gonyleptid species. In our study, rough pit glands were generally absent from the legs of agoristenid harvestmen, but present on the legs of most gonyleptids (Glysterus sp.…”

“…An ultrastructural study of porous and nonporous rough pit glands is needed to resolve this issue. On the basis of their relatively high abundance on multiple leg segments (present study) and the dorsal scutum (especially the ocularium: Rodriguez et al 2014), we hypothesize that rough pit glands may represent phylogenetically informative structures at the familial level. Within the Cosmetidae, the usefulness of rough pit glands (morphology or distribution) as characters for identifying genera or species is less clear.…”

“…The inclusion of characters based upon appendicular morphology along with others derived from SEMbased examinations (Rodriguez et al 2014, Fernandes & Willemart 2014 identified several informative characters based upon comparisons of the density, distribution and relative size of tubercles on the legs of gonyleptid harvestmen, but did not consider interspecific variation in microanatomy. Gainett et al (2014) identified three discrete appendicular characters that were useful in refining relationships at the superfamilial level among laniatorean harvestmen.…”

“…Recent studies of cosmetid harvestmen have identified a variety of structures that exhibit considerable interspecific variation. These characters include the general shape of the dorsal scutum (Kury et al 2007) (Rodriguez et al 2014).…”

“…Recent morphological studies using scanning electron microscopy (SEM) have revealed a diverse assortment of cuticular structures on the legs of gonyleptoidean harvestmen 43:194-206 including multiple types and different sizes of setae (Willemart & Gnaspini 2003;Willemart et al 2007), rough pit glands (Willemart et al 2007;Rodriguez et al 2014) single and clustered glandular openings Gnaspini & Rodrigues 2011;Fernandes & Willemart 2014), slit sensilla (Willemart et al 2007(Willemart et al , 2009a, granulations and ridges (Murphree 1988), and different shapes, densities, and sizes of tubercles (Willemart et al 2007(Willemart et al , 2009a. In addition to interspecific differences in microanatomy (reviewed by Willemart et al 2009a), variation in the distribution and morphology of setae on different legs and between leg segments has been observed (Willemart & Gnaspini 2003).…”