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Student Research Projects

A Scanning Electron Microscopy Survey of the External Morphology of Cosmetid Harvestmen

Student Andrea Rodriguez '14
Faculty Mentor(s) Dr. Victor Townsend
Department Biology
Course BIO 400: Scanning Electron Microscopy (SEM)

Abstract

The taxonomy of cosmetid harvestmen requires substantive revision, a major effort that could be aided through the identification of novel, informative characters. In this study, we used scanning electron microscopy to compare the microanatomical features of the ocularium, dorsal scutum, chelicera, pedipalp (femur and tibia), and sexually dimorphic regions of leg IV of 12 cosmetid harvestmen including multiple species for the genera Cynorta, Erginulus, and Paecilaema. We observed considerable interspecific variation with regards to the shape and microanatomy of the ocularium, surface texture of the dorsal cuticle, number and shape of cheliceral teeth, number, shape and distribution of tubercles on the femur of the pedipalp, and the size, shape and number of tubercles of male leg IV (femur, patella, tibia and metatarsus). In an attempt to determine which structures were synapomorphic for cosmetid harvestmen, we used compared the external morphology of the cosmetid taxa with that of six species of gonyleptoidean harvestmen representing the families Agoristenidae, Cranaidae, Gonyleptidae, Manaosbiidae, and Stygnidae. Our results indicate that the presence of circular structure on the ocularium and a microgranulate morphology on the dorsal scutum may be derived characters for the family that have not been previously identified.

 

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