ELONGATED PEDICILLATE SETAE: A PUTATIVE SENSORY SYSTEM AND SYNAPOMORPHY OF SPIDERS Ingi Agnarsson 1,4 , Jonathan A. Coddington 1 , and Laura J. May-Collado 2,3 : 1 Systematic Biology-Entomology, Smithsonian Institution, NHB-105, PO Box 37012, Washington, DC 20013-7012, USA; 2 Florida International University, Department of Biological Sciences, 11200 SW 8th Street, Miami Florida 33199, USA; 3 Universidad de Costa Rica, Escuela de Biologı ´a, Apto. 2060 San Pedro, Costa Rica ABSTRACT. We survey spiders from 43 families, 62 genera, and three arachnid outgroups for the presence and diversity of elongated pedicillate setae (EPS)—a complex system of probably sensory setae hitherto undocumented outside Theridiidae. Although not present in all spiders, these setae are sufficiently widespread to suggest they are primitively present in the order. Because they are absent in related arachnids, they appear to be a synapomorphy of spiders. Based on the morphology and orientation of these setae, it has been suggested that they supplement abdominal slit sensilla in proprioception, documenting the position and movement of the abdomen relative to the cephalothorax. Although still poorly known, the presence and distribution of these setae are informative at lower and higher phylogenetic levels. Keywords: Araneae, phylogeny, proprioreception Spiders are typically setose and many of the setae, especially on the appendages, are sensory (Seyfarth 1985; Barth 2001). However, the distribution and function of the many different kinds of setae on spider bodies are poorly known. Morphological, behavioral, histologi- cal, and neurobiological research are all neces- sary to understand setal distribution, function, and to establish interspecific homologies. Mor- phology can document apparently different types of setae and their distribution on indi- viduals as well as across species. It can also infer function from their detailed structure, distribution, and orientation. Agnarsson (2004) documented the distribution of distinct elon- gated setae around the pedicel on abdomens of theridiid spiders. The distribution of these setae was phylogenetically informative. They sur- round the pedicel and are juxtaposed to the cephalothorax so that abdominal movement is likely to cause flexion, which may, in turn, signal the relative positions of the abdomen and cephalothorax. He proposed the name ‘‘supra- pedicillate proprioceptive setae:’’ propriocep- tion (or proprioreception) is the perception of the body’s position and movement including physical displacement and any changes in tension, or force within the body (e.g., Seyfarth & Pflu ¨ gler 1984; Seyfarth 1985; Seyfarth et al. 1985). The proprioceptive hypothesis was based on the morphological, not behavioral, histological, and neurobiological evidence. Here we use a more neutral term, elongated pedicillate setae (EPS) although we hope that the hypothesis of proprioceptive function will be tested in future studies. Agnarsson’s (2004) survey was limited to theridiids and a few outgroups and his discussion focused mainly on their phyloge- netic utility within theridiids. Here we docu- ment the distribution of EPS and their potential as characters for higher level phylogenetic studies from a broader survey of spider families. METHODS Sixty-nine taxa were selected to span the order Araneae and closely related outgroups (many additional species, especially theridiids, were surveyed by Agnarsson 2004). Taxon representation was biased, however, towards Orbiculariae, and Theridiidae by the authors’ specialties. Given sufficient specimens, the abdomens were critical point dried, glued to a rivet, and sputter coated with Au/Pd. 4 Current address: Department of Biology, Univer- sity of Akron, Akron, Ohio 44325-3908, USA. E-mail: iagnarsson@gmail.com 2007 (2008). The Journal of Arachnology 35:411–426 411