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.

A descrição original desta espécie foi baseada numa única fêmea e nenhuma ilustração de seus órgãos reprodutivos foi apresentada. Após coletarmos alguns espécimes identificados como I. seladonium, decidimos redescrever esta espécie e descobrimos que o macho descrito por Mello-Leitão (1923) havia sido erroneamente identificado como pertencente a esta espécie. Assim, neste artigo, é descrito pela primeira vez, o macho de I. seladonium e pela primeira vez as genitálias do macho e da fêmea são detalhadamente ilustradas. Notas sobre o comportamento e a história natural de I. seladonium são apresentadas baseadas em dados de animais vivos observados no campo e em cativeiro. Foi observado um imaturo de I. seladonium construindo um abrigo convexo com pequenos pedaços de casca de árvore, comportamento desconhecido em Aviculariinae. Duas cortes foram observadas e fotografadas. Os comportamentos de tamborilar com as pernas; tamborilar com os pedipalpos do macho sobre o corpo da fêmea; e movimentos dorso-ventrais, do abdômen da fêmea, durante a inserção do êmbolo, são registrados pela primeira vez em Aviculariinae. O tempo médio de duração da corte e da cópula foi de aproximadamente dois minutos.

The original description of this species was based on a single female and no illustrations of reproductive organs were presented. After we collected several specimens identified as I. seladonium, we decided to redescribe this species and discovered that the male, previously described as belonging to this species, was misidentified by MELLO LEITÃO (1923). Thus, in this paper the male of I. seladonium is newly described and the reproductive organs of male and female are described and illustrated in detail. Notes on the behavior and natural history of I. seladonium are presented based on the observation of live specimens in the field and in captivity. An immature of I. seladonium was observed constructing a hinged retreat with silk and little pieces of bark, a behavior not previously seen for other Aviculariinae. Two courtship events were observed and photographed, leg tapping and palpal drumming of the male on female's body and dorsum-ventral movements of the female's abdomen while the male was inserting the embolus were documented to Aviculariinae for the first time. The courtships and mating lasted almost two minutes.