Spintharus is a genus of spiders that contained only two species until 2018 when it was demonstrated that a ‘widespread’ species was instead composed of multiple short-range endemics. This note redescribes Spintharus gracilis Keyserling and describes a new species of Spintharus (Araneae, Theridiidae), S. leverger sp. nov., both based on specimens from Brazil. We also examine specimens from several additional localities in Brazil displaying variation consistent with patterns previously found within the Caribbean: geographically isolated and unique localities may contain independent species lineages. Given the limited number of specimens, profuse variation, and lack of DNA data from museum specimens, it is challenging to gauge the number of species in the observed material. Instead of describing these as new species here, we highlight this variation and hypothesize that in South America, a greater diversity of the genus across the geographical landscape will be found than predicted based on Levi’s “widespread Spintharus flavidus” hypothesis. Our results suggest that continental efforts to sample the genus would be profitable, as this charismatic group likely harbors unappreciated diversity throughout the continent.

Biogeography, cobweb spiders, cryptic species, DNA barcoding

American cobweb spiders (Theridiidae) were revised by Herbert Levi in numerous taxonomical treatises throughout the 1950s and 1960s (e.g. Levi 1954, 1955, 1959, 1963a, b). Many of the genera, including Spintharus, were subsequently placed in morphological (Agnarsson 2004) and molecular phylogenetic analyses (Arnedo et al. 2004, Liu et al. 2016), largely supporting Levi’s work. In his deliberate and practical treatment of all American araneids, tetragnathids, and theridiids Levi addressed the genus Spintharus in two papers (Levi 1954, 1963a). Therein he redescribed S. gracilis Keyserling from Brazil, and concluded that only one other species could be recognized: S. flavidus Hentz that he characterized as an “extremely variable” and widespread species (Levi 1954: 81). As indicated by later molecular work and systematic revisions (Dziki et al. 2015, Agnarsson et al. 2018), the profuse variation described by Levi appears to represent a large species complex, rather than one or a few highly variable species. However, the morphological variation makes organization into species level bins challenging, and some related species are arduous to diagnose based on morphology alone. Hence, Agnarsson et al. (2018) relied heavily on molecular diagnoses, utilizing DNA barcodes.

To date, only taxa from the Caribbean region have been revisited since Levi’s revisions, but here we examine samples made available by loan from Brazil provided by the Museu de Ciências e Tecnologia Pontifícia (MCTP), Rio Grande do Sul. We find clear morphological differences between some of the specimens found at different locations, suggesting that the pattern found throughout the Caribbean of diverse, potentially speciose groups remaining undescribed will likely hold on the South American continent as well. Here, we redescribe S. gracilis, and describe a new species in order to call attention to likely overlooked diversity and the need for extensive sampling of fresh DNA grade material of the genus across South and Central America.

Specimens were deposited in the following collection: MCTP, Coleção de Aracnídeos, Porto Alegre (curator: Renato Augusto Teixeira) and the Smithsonian Museum of Natural History (SMNH), Arachnida and Myriapoda collection, Washington DC (curator: Hannah Wood). We attempted DNA extraction and amplification of DNA barcodes from legs of borrowed specimens preserved in ethanol, however this yielded no viable DNA. Specimens were then mounted for photography by being partially submerged in a Petri dish of ethyl alcohol gel (hand sanitizer) for stabilization, and then fully covered with liquid ethyl alcohol to prevent glare. Photographs were taken in the dorsal, ventral, and lateral views of the specimen with a Canon 5D camera with a 65mm macro zoom lens. Multiple photographs taken with a narrow depth of field were combined using Helicon Focus software to present a single photograph of the entire specimen in detail. Measurements were performed in Adobe Photoshop using camera lens and zoom magnification to determine scale. Epigyna were photographed before being dissected from the specimen. Soft tissue was then dissolved using a diluted potassium hydroxide solution and cleared epigyna were photographed in ventral and dorsal views. Left male pedipalps were removed before being photographed. Diagnostic descriptions of abdominal morphological features follow (Agnarsson et al. 2018).

The recent phylogenetic analysis of Spintharus (Dziki et al. 2015) and subsequent naming of 15 new species (Agnarsson et al. 2018) has shown a previously underestimated diversity in the genus. The varying morphology of specimens found in Brazil alone suggests there remain a number of additional species to be found in the New World. Among the specimens examined, we found a number of putative species. However, absent DNA data was shown to be critical for diagnoses in this genus by Dziki et al. (2015), and with color patterns – also putatively informative for taxonomy – eroded by ethanol, we opted to highlight this newly discovered diversity by redescribing the only known species from Brazil, S. gracilis, and naming a single new species. We chose to describe this species because it is clearly morphologically distinct, and with sufficient material available of both sexes for an accurate description.

Given geographical variation observed in the samples here, and the clear patterns from the Caribbean of short-range endemics, we expect additional sampling of fresh DNA grade material throughout South America to lead to the discovery of very numerous new species. Thus, South American Spintharus could emerge as a radiation of charismatic mesofauna with obvious conservation implications and a great potential tool to further understanding of biogeographical patterns in the Americas. Spintharus also holds promise as a potentially rich study system in the evolution of color patterns and polymorphism.

Thanks to Arno Lise for arranging specimen loan from Museu de Ciências e Tecnologia Pontifícia. Lisa Chamberland assisted with photography work. Antonio D. Brescovit provided useful comments on the manuscript. This research was funded by NSF grant (DEB-1050187-1050253) to IA and G. Binford and (DBI-1349205) to D. Barrington, IA, and C.W. Kilpatrick.