Microstructure of the silk apparatus of the comb‐footed spider, Achaearanea tepidariorum (Araneae: Theridiidae)

Abstract

The microstructural organization of the silk‐spinning apparatus of the comb‐footed spider, Achaearanea tepidariorum, was observed by using a field emission scanning electron microscope. The silk glands of the spider were classified into six groups: ampullate, tubuliform, flagelliform, aggregate, aciniform and pyriform glands. Among these, three types of silk glands, the ampullate, pyriform and aciniform glands, occur only in female spiders. One (adult) or two (subadult) pairs of major ampullate glands send secretory ductules to the anterior spinnerets, and another pair of minor ampullate glands supply the median spinnerets. Three pairs of tubuliform glands in female spiders send secretory ductules to the median (one pair) and posterior (two pairs) spinnerets. Furthermore, one pair of flagelliform glands and two pairs of aggregate glands together supply the posterior spinnerets, and form a characteristic spinning structure known as a “triad” spigot. In male spiders, this combined apparatus of the flagelliform and the aggregate spigots for capture thread production is not apparent, instead only a non‐functional remnant of this triad spigot is present. In addition, the aciniform glands send ductules to the median (two pairs) and the posterior spinnerets (12–16 pairs), and the pyriform glands feed silk into the anterior spinnerets (90–100 pairs in females and 45–50 pairs in males).

Microstructure of the silk spigots of the green crab spider Oxytate striatipes (Araneae: Thomisidae)

“…In O. striatipes , the ampullate spigots are located on both the anterior and the posterior spinnerets, and the total four pairs of ampullate spigots send secretory ductules to both the anterior and the median spinnerets. This arrangement of the ampullate spigot has been commonly reported in most araneid spiders except for a peculiar modification in Theridiidae spiders (Moon & An 2006). It has also been reported that the two kinds of ampullate gland (major and minor) in araneid spiders produce different types of silk material (Tillinghast & Christenson 1984; Tillinghast & Townley 1986, 1987).…”

“…Previous studies have found that divergence of spider species correlates with evolution of the ampullate gland (Foelix 1996), and it has also been shown that selection and molecular events resulted in the evolution of the ampullate silk proteins (Craig & Riekel 2002). Like other araneid spiders, such as wandering spiders (Moon 1998; Moon & An 2005) and other web‐building spiders (Tillinghast & Townley 1986; Peters & Kovoor 1991; Moon 2002; Park & Moon 2002; Moon & Tillinghast 2004; Moon & An 2006), the ampullate glands were the largest silk glands observed in O. striatipes and were used for making draglines.…”

“…It is known that functional specialization of the silk‐producing apparatus involves precise modifications of the shape of the spinnerets, the number and morphology of the spigots, and the anatomical characteristics of the silk glands (Peters 1987; Shear 1994). Variations in the composition of the spinning apparatus of araneid spiders have been studied by many researchers (Coddington 1986; Kovoor 1987; Nentwig & Heimer 1987; Peters & Kovoor 1991; Park & Moon 2002; Moon & Kim 2005; Moon & An 2006).…”

Cupiennius salei and Achaearanea tepidariorum: Spider models for investigating evolution and development

“…Comparison of Cupiennius and Achaearanea adult female silk glands. Differences between the glands of these species and glandular differences between spinnerets within one animal from our own and previous observations (87,100) are illustrated. Different gland types are distinguished on morphological and histochemical grounds, i.e.…”

Cobweb-weaving spiders produce different attachment discs for locomotion and prey capture

“…To test the possibility that the pyriform fibres in the scaffolding and gumfoot discs could be chemically different, we cite the work of Moon et al 9 that shows that female A. tepidariorum spiders possess 90-100 pairs (total 180-200) of pyriform glands that feed into discrete pyriform spigots on the anterior spinnerets. The total number of pyriform spigots is consistent with the total number of fibres measured by us in the gumfoot discs (188 ± 20).…”