Summary 1.Frequency of singletons -species represented by single individuals -is anomalously high in most large tropical arthropod surveys (average, 32%). 2. We sampled 5965 adult spiders of 352 species (29% singletons) from 1 ha of lowland tropical moist forest in Guyana. 3. Four common hypotheses (small body size, male-biased sex ratio, cryptic habits, clumped distributions) failed to explain singleton frequency. Singletons are larger than other species, not gender-biased, share no particular lifestyle, and are not clumped at 0·25-1 ha scales. 4. Monte Carlo simulation of the best-fit lognormal community shows that the observed data fit a random sample from a community of ~700 species and 1-2 million individuals, implying approximately 4% true singleton frequency. 5. Undersampling causes systematic negative bias of species richness, and should be the default null hypothesis for singleton frequencies. 6. Drastically greater sampling intensity in tropical arthropod inventory studies is required to yield realistic species richness estimates. 7. The lognormal distribution deserves greater consideration as a richness estimator when undersampling bias is severe.

This study revises the taxonomy, biology, phylogeny, and biogeography of the basal‐most nephilid spider lineage, the Clitaetrinae, with the least known nephilid genus Clitaetra. The five previously known species are redescribed: Clitaetra clathrata Simon from western Africa, C. simoni Benoit from central Africa, C. episinoides Simon from the Comoro Islands and Mayotte, C. perroti Simon from Madagascar, and C. thisbe Simon from Sri Lanka with first descriptions of the males of C. clathrata and C. perroti. Additionally, C. irenae sp. nov. is described in both sexes from southern Africa. Clitaetra biology, so far largely unknown, is presented here based on observations of C. irenae in South Africa, and clitaetrine anatomy is summarized to assess phylogenetic homologies. A species‐level phylogenetic analysis of 32 taxa scored for 197 morphological and behavioural characters results in eight most parsimonious cladograms and places Clitaetra as sister to the clade (Herennia+ (Nephilengys+Nephila)). Thus, the orb‐weaving spider family Nephilidae Simon contains the (sub)tropical genera Nephila, Nephilengys, Herennia, and Clitaetra, but not Deliochus or Phonognatha. Contra recent cladistic treatments, the nephilines are not tetragnathids, but the sister group to the newly proposed clade, Nephilidae, is ambiguous. The three species clades (subgenera) within Clitaetra show a seemingly old Gondwanan biogeographic pattern: Afroetra subgen. nov., with the three mainland African species, is sister to Clitaetra with the two Indian Ocean island species. Indoetra subgen. nov. contains the unstudied species from Sri Lanka, C. thisbe. Future understanding of the morphology and biology of C. thisbe is important for the polarization of many nephilid features. Vicariance would estimate the clitaetrine subgeneric clades and basal nephilid lineages to be at least 160 Myr old and of Gondwanan origin.

The Pantropical spider clade Nephilidae is famous for its extreme sexual size dimorphism, for constructing the largest orb-webs known, and for unusual sexual behaviors, which include emasculation and extreme polygamy. We synthesize the available data for the genera Nephila, Nephilengys, Herennia and Clitaetra to produce the first species level phylogeny of the family. We score 231 characters (197 morphological, 34 behavioral) for 61 taxa: 32 of the 37 known nephilid species plus two Phonognatha and one Deliochus species, 10 tetragnathid outgroups, nine araneids, and one genus each of Nesticidae, Theridiidae, Theridiosomatidae, Linyphiidae, Pimoidae, Uloboridae and Deinopidae. Four most parsimonious trees resulted, among which successive weighting preferred one ingroup topology. Neither an analysis of an alternative data set based on different morphological interpretations, nor separate analyses of morphology and behavior are superior to the total evidence analysis, which we therefore propose as the working hypothesis of nephilid relationships, and the basis for classification. Ingroup generic relationships are (Clitaetra (Herennia (Nephila, Nephilengys))). Deliochus and Phonognatha group with Araneidae rather than Nephilidae. Nephilidae is sister to all other araneoids (contra most recent literature). Ethological data, although difficult to obtain and thus frequently missing for rare taxa, are phylogenetically informative. We explore the evolution of selected morphological and behavioral characters, discuss and redefine the homology of palpal sclerites, disprove semientelegyny in spiders, trace the newly interpreted evolution of the orb web, and show that nephilid genital morphologies coevolve with sexual behaviors and extreme sexual size dimorphism. Phylogenetic interpretations of behavior suggest new insights into spider biology and avenues for future research.Ó The Willi Hennig Society 2007.Discovery of behavioral homologies has importance for biology and other human endeavors far beyond simply adding characters for phylogenetic analyses. Greene (1994) Golden orb-weaving spiders (Nephila) and hermit spiders (Nephilengys) are among the most prominent and most researched tropical arachnids (reviewed in Kuntner, 2005Kuntner, , 2006Kuntner, , 2007aHarvey et al., 2007). They are famous for extreme sexual size dimorphism in which males are many times smaller than the giant females