Ovipositor morphology of cosmetid harvestmen (Arachnida, Opiliones, Laniatores): a new source of informative characters.

The external morphology of the penis is an important source of systematic characters in phylogenetic studies of harvestmen. Modern taxonomic studies generally include micrographs generated by scanning electron microscopy (SEM) to illustrate penis morphology. In contrast, the external morphology of the ovipositor has largely been ignored for harvestmen belonging to the suborder Laniatores. Comparative studies of ovipositor microanatomy using SEM are especially lacking for species belonging to the superfamily Gonyleptoidea. In an effort to determine if the ovipositor could be a useful source of informative characters for these harvestmen, we investigated interspecific variation in the external morphology of the ovipositor for 14 species from the family Cosmetidae. Our SEM-based study revealed that the external surface of the distal tips of the ovipositors of most species was generally divided into four symmetrical lobes, although we observed a bilobed condition in Erginulus clavotibialis and Erginulus subserialis. The distal surfaces were also generally smooth, with the exception of the ovipositor of Erginulus weyerensis, which featured small surface setae. In addition, we observed considerable interspecific variation in the morphology of the peripheral setae on the distal tip, especially with respect to relative size, morphology of the shaft, and number, symmetry, and shapes of the distal tips. The functional significance, if any, of variation in the structure of the peripheral setae is unclear. Additional behavioral studies of copulation and oviposition are needed to determine the functional relationships between reproductive morphology and behavior. The morphological variation that we observed suggests that future taxonomic studies of cosmetid harvestmen, and potentially other gonyleptoidean taxa, would benefit from the inclusion of descriptions of ovipositor morphology.