A new species of Goeldia Keyserling, 1891 is described. Goeldia is the only genus of Titanoecidae with species in the Neotropical region and includes eight species diagnosed by the presence of a patellar process in the male palp. The new species, Goeldia zyngierae sp. nov., was found living inside the Casa de Pedra cave, Ribeira, Itabaiana, Sergipe, Brazil. Goeldia zyngierae sp. nov. is diagnosed by the tegular process with a small constriction near the base of the dorsal part and by a distal narrowing, more visible in the dorsal side of the patellar process of the male palp. The female epigynum shows a pair of sinuous depressions and a large mid field that does not close the copulatory openings as in Goeldia luteipes Keyserling, 1878. The vulva presents a narrow and straight copulatory duct in comparison with those of Goeldia mexicana Pickard-Cambridge, 1896 and a narrow spermathecae. The description includes illustrations of the genital organs, measurements of the body and legs and leg spination. Notes on the natural history show that inside the cave the spiders live farther than the first 40 m, in the aphotic zone, under stones or on the wall. They were never observed alone or walking on the ground, and the webs contained two to thirty spiders of different life stages, living together, suggesting a possible cooperative behavior. Further field work is needed to confirm and understand the degree of sociability of this new species, if this species is restricted to caves, and if this behavior occurs only inside the caves.

Foram estudadas a seleção de microhabitat e co-ocorrência de Pachistopelma rufonigrum Pocock (Theraphosidae) e Nothroctenus fuxico sp. nov. (Ctenidae) em bromélias-tanque. A condição da temperatura dentro e fora das plantas foi medida para verificar se a temperatura da água acumulada dentro da bromélia afeta algum aspecto comportamental das aranhas que ali vivem. Medidas dos parâmetros foliares foram realizadas para avaliar se a estrutura das plantas chega a afetar a abundância ou a seleção de microhabitat dessas aranhas. Aparentemente, as diferenças na estrutura das duas espécies de bromélias estudadas não afetam nem a abundância, nem a seleção de microhabitat de P. rufonigrum e N. fuxico sp. nov. A preferência e co-ocorrência de ambas as espécies de aranhas parece ser um evento ao acaso. Adicionalmente, apresenta-se notas sobre os limites de distribuição de P. rufonigrum e descreve-se N. fuxico sp. nov. do Estado de Sergipe, Brasil.

Microhabitat selection and co-occurrence of Pachistopelma rufonigrum Pocock (Theraphosidae) and Nothroctenus fuxico sp. nov. (Ctenidae), in tank bromeliads were investigated. Thermal conditions, inside and outside the plants, were measured in order to verify if the temperature of the water that accumulates inside the plant affects the behavior of these species. Measurements of foliar parameters were taken in order to evaluate if and how plant structure affects spider abundance and microhabitat selection. Apparently, differences in plant structure do not affect either spider abundance or microhabitat selection. No microhabitat preference was observed and co-ocurrence of both species was a random event. In addition, notes on the distribution range of P. rufonigrum and the description of N. fuxico sp. nov. from State of Sergipe, Brazil are presented.

Pachistopelma rufonigrum Pocock, 1901 apresenta mudanças ontogenéticas no seu padrão de coloração. Após emergirem dos ovos, as pequenas aranhas são azuladas, com nuances metálicas. Os juvenis possuem uma listra negra na região central do dorso do abdômen orientada no sentido vertical e três listras negras no dorso do abdômen orientadas horizontalmente. Os adultos são totalmente negros. Acredita-se que a diferença na coloração entre indivíduos de instares diferentes dentro de uma mesma espécie seja uma estratégia para se evitar a competição intraespecífica.

Pachistopelma rufonigrum Pocock, 1901 presents ontogenetic changes of its coloration pattern throughout its development. After emergence from the eggs, spiderlings are bluish, with metallic and/or iridescent nuances. The juveniles have a vertically directed black stripe in the central region of abdomen dorsum and three horizontally directed black stripes in the abdomen dorsum. Adults are completely black. These coloration differences between juveniles and adults of the same species appear to be a strategy to avoid the intraspecific competition.

Aspects of the behavior of the theraphosid spider Pachistopelma rufonigrum, in two species of tank bromeliads in an area with white sands in the Serra de Itabaiana, Sergipe, Brazil, are described. Observations on habitat, microhabitat, foraging, ecdysis and reproduction, were made. Our data suggested that P. rufonigrum inhabits only these species of bromeliads, since all stages of the life cycle were observed in the plant. The relationships degrees between P. rufonigrum and the species of studied tank bromeliads are discussed.