Comparative Study of the Microanatomy of Four Species of Harvestmen (Opiliones, Eupnoi)

Abstract

Most species descriptions of harvestmen from Central America that belong to the suborder Eupnoi are based on characters such as total body length, relative size of leg segments, coloration of the body and legs, and armature of the eye mound and dorsal scutum. Characters based on reproductive morphology and microanatomical structures are generally absent from most taxonomic works. Not surprisingly, the taxonomy of these harvestmen from this region requires extensive revision. In an effort to identify novel characters, we used scanning electron microscopy to compare the morphology of somatic and reproductive structures of Prionostemma vittatum (Roewer, 1910), Metopilio niger (Goodnight and Goodnight, 1942), and Metopilio ornatipes (Banks, 1909). Specifically, we investigated the morphology of the ocularium, ozopore, dorsal scutum, genital plate, pedipalp, spiracular opening on tibia II, ovipositor, and penis. We compared the morphology of these Neotropical taxa with that of a temperate sclerosomatid species, Leiobunum formosum (Wood, 1870). In general, we observed interspecific variation in the surface texture of the cuticle and the distribution of setae on the body and appendages. Potentially informative characters include cuticular structures associated with the ocularium, anterior propeltidium, meso- and metapeltidium, dorsal scutum, genital plate, pedipalp, and penis. We also observed intersexual variation with respect to morphology of Spicer's tarsal organ and the claw of the pedipalp.

External Morphology of Pyza taurica Gruber, 1979 (Arachnida: Opiliones)

“…The harvestmen or harvest spiders belong to arthropods; their cuticle, like other arthropods, is the substrate to cuticular structures and sense organs are of great importance for obtaining environmental information (Spicer, 1987;Willemart & Gnapsini, 2003;Willemart, Chelini, Andrade, and Gnaspini, 2007;Willemart & Giribet, 2010;Rodriguez, Townsend, & Pround, 2014). Many scanning electron microscopic and light microscopic studies on the integument of arachnids have been carried out in the world (Pittard & Mitchell, 1972;Barth & Stagl, 1976;Igelmund, 1987;Spicer, 1987;Willemart & Gnaspini, 2003;Willemart et al, 2007; Yigit, Bayram, Çorak, & Danışman, 2007;Willemart & Giribet, 2010).…”

“…The most important characters such as reproductive morphology and microanatomical structures are generally absent from most taxonomic works. For this reason, to identify novel characters, scanning electron microscopic studies are important (Rodriguez et al, 2014).…”

Ontogenetic variation in the sensory structures on the pedipalps of cosmetid harvestmen (Arachnida, Opiliones, Laniatores)

“…In addition to apophyses, tubercles and ridges, there are a variety of other cuticular associated with the segments of the pedipalps of harvestmen including sensilla chaetica, trichomes, glandular setae, slit sensilla, and pores (Spicer, ; Willemart, Farine, & Gnaspini, ; Wolff et al, ). Sensilla chaetica insert into prominent sockets (Rodriguez, Townsend, & Proud, ; Willemart et al, ). There is considerable interspecific variation in the size and distribution of these setae on the pedipalp.…”

“…In addition to setae, the pedipalps of harvestmen may also feature slit sensilla (used in proprioreception: Willemart et al, ) and an abundance of pores, especially on the patella and tarsus (Wolff et al, ). In eupnoid harvestmen, Spicer's tarsal organ refers to a group of pores that occur among a row of microdenticles, usually on the ventral surface of the tarsus of the pedipalp (Rodriguez, Townsend, & Proud, ; Spicer, ; Willemart et al, ).…”