Field Guide to the Spiders of California and the Pacific Coast States by Adams Richard J.; Manolis Timothy D. ;

Author:Adams, Richard J.; Manolis, Timothy D. ;
Language: eng
Format: epub
Publisher: University of California Press

* * *

PIMOIDAE

Pl. 24

IDENTIFICATION: Pimoidae is a small family of eight-eyed entelegyne spiders that is part of a larger superfamily called Araneoidea. This superfamily contains some of our most common spider families, including the cobweb weavers (Theridiidae), the orb web weavers (Araneidae), and the sheet web weavers (Linyphiidae).

With one very rare exception, pimoids range from 5 to 12 mm (.2 to .47 in.) in length. Most have exceptionally long, moderately spined, reddish-brown legs that are coated with setae and demonstrate patella-tibial autospasy, an adaptation that allows the leg to break away at the patella-tibia joint when grabbed. Members of the genus Pimoa have dark, oval abdomens decorated with assorted light chevrons, spots, and stripes. Their cephalothoraxes have conspicuous pit-like thoracic furrows and are tan to mahogany brown with dark markings around the eyes and midline. Pimoa also have robust chelicerae with stridulatory files along the lateral face. With experience, you will find it fairly easy to recognize the larger Pimoidae in their messy, extensive sheet webs. The identification of an individual away from its web, however, may require focusing on the structure of its reproductive organs and mouthparts as described in Ubick (2005c).

The exception with respect to many of these features is the extremely rare Nanoa enana. Known only from Northern California and southern Oregon, this tiny spider is only around 1.5 mm (.06 in.) in length, has very few to no spines on its legs, and has small, weak chelicerae without stridulatory files. Its placement within Pimoidae was only possible after a detailed examination of its reproductive structures by Hormiga et al. (2005).

SIMILAR FAMILIES: Pimoids are closely related to the sheet web weavers (Linyphiidae) and, for the most part, share many of same features, including their basic web architecture, prominent leg spination, and patella-tibia autospasy. While the clearest traits that differentiate these two families are based on the structure of their reproductive organs, other features can be useful. Overall, sheet web weavers are generally quite small, rarely exceeding 5 mm (.2 in.) in length. Additionally, the region’s largest linyphiid genera, Neriene and Frontinella, build complex, fine-meshed domed or multilevel webs. Members of the genus Calymmaria (Hahniidae) look like pimoids and share many of the same habitats. However, Calymmaria build conical, basketlike sheet webs and have significantly reduced or missing coluli. On Pimoa, the colulus is large and clearly visible between the anterior lateral spinnerets. Additionally, Calymmaria lack stridulatory files on their chelicerae and are unable to perform patella-tibia autospasy.

The highly unusual N. enana was not described when Ubick et al. (2005) went to press, and the familial placement of a specimen would be impossible using its key. The inclusion of N. enana in Pimoidae was based on the structure of its complex reproductive organs, the details of which can be found in Hormiga et al. (2005).

PACIFIC COAST FAUNA: Two genera representing 14 regional species. By far the largest and most visible of the Pacific coast’s two pimoid genera is Pimoa (pl. 24). With 13 species known from both coastal and mountain forests, Pimoa are conspicuous members of the Pacific Northwest’s araneofauna.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.