Abstract
Spider capture silk is a natural scaffolding material that outperforms most synthetic materials in terms of its combination of strength and elasticity. Among the various kinds of silk threads, cribellar thread is the most primitive prey-capturing type of spider web material. We analyzed the functional organization of the sieve-like cribellum spigots and specialized calamistral comb bristles for capture thread production by the titanoecid spider Nurscia albofasciata. The outer cribellar surface is covered with thousands of tiny spigots, and the cribellar plate produces non-sticky threads composed of thousands of fine nanofibers. N. albofasciata cribellar spigots are typically about 10 μm long, and each spigot appears as a long individual shaft with a pagoda-like tiered tip. The five distinct segments comprising each spigot is a defining characteristic of this spider. This segmented and flexible structure not only allows for spigots to bend individually and join with adjacent spigots, but it also enables spigots to draw the silk fibrils from their cribella with rows of calamistral leg bristles to form cribellar prey-capture threads.
Highlights
Araneomorph spiders can be classified as cribellate or ecribellate based on the presence or absence, respectively, of a cribellum in addition to multiple spinnerets (Coddington and Levy 1991)
The cribellum is a silkspinning organ consisting of single or multiple plates covered by thousands of minute spigots, which produce fine fibrils that are quickly hackled by the calamistrum, producing woolly-structured silk (Foelix 2011)
Two types of silk spigots the major ampullate gland and the pyriform gland spigots were distributed on the anterior lateral spinneret (Fig. 1b, c)
Summary
Araneomorph spiders can be classified as cribellate or ecribellate based on the presence or absence, respectively, of a cribellum in addition to multiple spinnerets (Coddington and Levy 1991). The cribellum is a silkspinning organ consisting of single or multiple plates covered by thousands of minute spigots, which produce fine fibrils that are quickly hackled by the calamistrum, producing woolly-structured silk (Foelix 2011). Cribellar silk has dry-adhesive properties and originates from cribellar fibrils spun from cribellar spigots (Opell 1995, 1999). The fibers are extremely fine, which facilitates prey entanglement, disengagement, and capture without the need for adhesive substances (Opell 2002; Hawthorn and Opell 2003). Cribellate web production is considered an expensive capture technique because of the extensive labor required to comb and deposit cribellar silk (Opell et al 2000; Opell and Schwend 2009). Cribellar silk improves is advantageous because it facilitates prey
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