Posterior Spinnerets Research Articles

First record of the spider family Hersiliidae (Araneae) from the Mesozoic of Europe (Bakony Mts, Hungary)

An adult male Hersiliidae spider is described from amber that originates from the Upper Cretaceous (Santonian) Ajka Coal Formation (Ajka-Csingervölgy, Hungary), the so-called ajkaite. The spider has elongate posterior spinnerets and a short third pair of legs III, both characteristics of the family, but differs from all known Mesozoic (discovered in burmite) and fossil and Recent European representatives of Hersiliidae so that a new genus and species name is proposed for Hungarosilia verdesi gen. et sp. nov. The new taxon is distinguishable by the following unique combination of characters: pro- and opisthosoma nearly circular in dorsal view; posterior spinnerets with a distal article more than three times longer than the basal article; pedipalpal tibia and patella short and stout but pedipalpal femur as long as the cymbium, cymbium egg-shaped and without cymbial apophysis; bulbus of circular shape in ventral view and slightly flattened is lateral view. The fossil represents the first record of Hersiliidae from the Mesozoic of Europe and establishes the second record of this family in the Mesozoic Era. The estimated paleoclimate and paleoflora of the Ajka coal sub-basin correspond well with habitat preferences of Recent relatives that are often arborical and found in association with tree bark. Overall, our findings highlight the importance of a neglected amber type, the ajkaite, for documenting and studying the European arthropod fauna during the Mesozoic.

Argiope bruennichi (Scopoli, 1772) Örümceğinin Ağ Yapısı ve Örü Aygıtının Morfolojisi

Örümcekler, omurgasız hayvanlar içinde karasal hayata en iyi şekilde uyum sağlamış gruplardan birisidir ve dünya üzerinde yaklaşık 48.000 tür ile temsil edilmektedir. Her ne kadar bütün örümcekler ağ örmeseler de örümceklerin ağları tam anlamıyla bir sanat eseridir. Örümceklerin ağ örmesindeki başlıca sebep avlanmaktır. Doğadaki bazı örümcek türleri ağlara bağımlı olarak yaşarken bazıları ağlara bağımlı olmayarak yaşamlarını sürdürürler. Temel taksonomik özellikler genellikle değişmeden kalmasına rağmen, bazı örümceklerin ağ örme aygıtları adaptif varyasyonlara uğrayabilirler. Bu çalışmada, oldukça dikkat çekici ağ örücü bir örümcek olan Argiope bruennichi‘nin (Scopoli, 1772) ağ yapısı ve ağ örü aygıtının yapısal organizasyonu, taramalı elektron mikroskobu (SEM) kullanılarak incelenmiştir. A. bruennichi‘nin ağ yapısı, örü memeleri özellikle posterior örü memeleri ve spigotların düzenlenmesi gösterilmiş ve elde edilen veriler literatür ışığında tartışılmıştır.

Hers and his: Silk glands used in egg sac construction by female spiders potentially repurposed by a \u2018modern\u2019 male spider

Cylindrical silk gland (CY) spigots distinguish a large clade of modern spiders, the CY spigot clade, which includes all entelegyne spiders and their closest relatives. Following a widespread paradigm, CYs and their spigots are only known to occur in female spiders and they produce silk used in the construction of egg sacs. Here we report the occurrence of a CY spigot or CY nubbin on each posterior median spinneret (PMS) in males (5th stadium and later) of the spider Australomimetus maculosus. Late juvenile males had a CY spigot on each PMS, whereas adult males either had a CY spigot or, more often, a non-functional CY nubbin. This indicates that potential CY use by males is at least largely limited to late juvenile instars and is not involved with egg sac construction. Despite the presence of CY spigots in both sexes, sexual dimorphism with respect to CYs was still evident since males lacked the CY spigot on each posterior lateral spinneret present in late juvenile and adult females, and CY spigots of males never had the wide shaft and opening of adult females. This study adds to our knowledge of spinning apparatus variability in modern spiders and demonstrates an exception to the paradigm that, in the CY spigot clade, such spigots are restricted to female spiders.

Wet‐to‐Dry Hybrid Spinning of Graphene Fiber Inspired by Spider Silk Production Mechanisms

AbstractThis study describes a graphene oxide (GO) fiber spinning method that produces a nearly 100% yield for converting a GO suspension into fibers. The fiber formation method is inspired by the spider silk spinning strategy. The dissolved silk protein, spidroin (wet state), is extruded and shear‐thinned through a posterior spinneret, exposing the silk to a dry state for curing. The wet‐to‐dry conversion in a spider spinneret enables nearly all the fiber precursor, spidroin, to be fabricated into a silk fiber with no loss of protein. Inspired by the process, a “wet‐to‐dry” hybrid spinning of GO is developed in which nearly all GOs are converted into fiber. At the liquid–liquid interface of two droplets containing GO and polyethyleneimine, the two oppositely charged components bind to each other in the wet state. Subsequently, one component touches and pulls the interfacial mixing point of the two droplets, forming a vertical, thin liquid column in which GO complexes experience shear force and directionally align into a thin fiber. Compared to existing wet‐spinning methods, this wet‐to‐dry method is highly energy efficient in terms of the simple procedure, lack of waste chemicals, and nearly 100% conversion of GO precursors.

Anaxibia folia spec. nov.-a new litter-dwelling dictynid spider from India (Araneae: Dictynidae: Dictyninae).

The dictynid genus Anaxibia Thorell, 1898 currently has six nominal species distributed in the Oriental and Ethiopian regions (World Spider Catalog 2017). The genus represents tiny to small spiders characterised by a reduced cribellum, long, cylindrical anterior and posterior spinnerets, cymbium with caudal modification, palpal patella with dorsal horn, sub-apically arising embolus, conductor with wide lamellar apex and simple female genitalia (Lehtinen 1967). The genus has one representative in India: Anaxibia rebai (Tikader, 1966), originally described under Dictyna Sundevall, 1833 (Tikader 1966; Lehtinen 1967). In this paper, we describe and illustrate a new litter-dwelling Anaxibia species collected from the Kerala state of southern India.

Recluse spiders produce flattened silk rapidly using a highly modified, self‐sufficient spinning apparatus

AbstractArthropod silk is among the most remarkable materials produced by animals, and is diverse in chemical composition and strand morphology. Different types of silk are produced by different spinning processes, and spiders show the greatest diversity in both. Extremely flattened silk strands with exceptional properties are spun by recluse spiders (Loxosceles spp.) using a single pair of spigots, but this spinning process remains unknown. We here combine movies, electron microscopy, and X‐ray microscopy to investigate how Loxosceles laeta spin their peculiar silk. We found that L. laeta show a unique weaving behaviour: the two anterior lateral spinnerets move very rapidly (8.5–13 times per second), each spinning a single strand of silk that is held by the posterior spinnerets; the silk is never pulled with the legs. Outgroup comparison with closely related spider families reveals that recluse spiders have a highly modified spinneret morphology, with elongate anterior spinnerets, a diastema between the spinnerets, modified setae that possibly help holding the silk strands, and long and thin muscles associated to the spinnerets. In contrast to all other arthropods, these morphological specializations allow them to rapidly spin without using the legs or the substrate – revealing the first self‐sufficient spinning apparatus in arthropods. This explains how a dense, sticky silk can be constructed from a single pair of spigots in a fast manner.

Pseudonemesia tabiskey, a new species of Pseudonemesia Caporiacco 1955 and new ultramorphological data for the Microstigmatinae (Araneae: Microstigmatidae)

ABSTRACTPseudonemesia tabiskey sp. nov. is described from an Andean Forest in Trujillo, Venezuela. The new species is the third for the genus and differs from the other two species by the presence of one short and apically rounded modified seta on the retrolateral distal portion of the male tibia I and clavate setae on the dorsal and lateral sides of abdomen in both sexes. A new diagnosis is given to Pseudonemesia and new morphological data based on scanning electron microscopy for the Microstigmatinae are presented. The presence of posterior median spinnerets in Pseudonemesia is discussed.

Funnel-web construction and estimated immune costs inAglaoctenus lagotis(Araneae: Lycosidae)

Constructing webs for survival is rare in wolf spiders. However, some species, postulated as basal in the family, live in funnel-webs. Aglaoctenus lagotis (Holmberg 1876), a South American lycosid, lives permanently in webs. It is virtually unknown how web construction occurs for this species and the few other lycosid weavers. Also, costs associated with construction have not been studied, although funnels are suggested to be particularly costly webs. This study describes the funnel-web construction behavior of A. lagotis (Lycosidae: Sosippinae) and measures its costs in subadult and adult individuals. We recorded web construction, effects of sealing spinnerets in weaving activity, and immune costs of weaving (measuring melanization of an implant) in individuals allowed to weave and prevented from weaving. Construction consisted of three alternating behaviors: deposition of thick threads with a radial orientation and prolonged attachments (mainly involving the anterior spinnerets); deposition of swaths of fine threads without consistent orientation and with short attachments (mainly involving the posterior spinnerets); and motionlessness. No sticky threads are present in the web. The thick threads have a supporting function and the fine threads have a filling function. Subadults and males allowed to weave reduced their immune response compared with those prevented from weaving; no such relationship was observed for females. Males presented the weakest immune response, followed by subadults and females. The web construction process showed greater similarity with agelenid spiders than with the only other lycosid studied, Sosippus janus Brady 1972, and appears to be a costly activity, especially for males.

A new species of the genus Atypus Latreille, 1804 (Araneae: Atypidae) from Korea.

Worldwide, 30 species of the genus Atypus Latreille, 1804 have been recorded from the United States, Europe, Africa, south-east and far-east Asia (Platnick 2014). Atypid spiders are characterized by a male sternum with marginal ridges, a short, straight and spike-like embolus, a straight conductor and a distally widened vulva with bulbous or pyriform receptacula and with two lateral patches of pores on the genital atrium (Gertsch and Platnick 1980). Kraus and Baur (1974) utilized various taxonomic characters to distinguish between the European species, such as the segmentation of the posterior spinnerets, features of the patellar membrane, morphology of sigilla opposite coxae I and IV, and the male palpal conductor, palpal furrow and male metatarsal spines. The genus Atypus was reviewed by Schwendinger (1990) who redescribed 12 recorded species and discussed the granular texture on the male chelicerae and front legs, and the cymbial pit for distinguishing species. Among 30 Atypus spiders, 18 species are distributed in Far-East Asia; 12 species from China (Zhu et al. 2006), 5 species from Korea (Kim 1985; Namkung 1986, 2001; Kim et al. 2006), and 2 species from Japan (Bösenberg and Strand 1906; Tanikawa 2006).

Organization of the spinnerets and spigots in the orb web spider, Argiope bruennichi (Araneae: Araneidae)

AbstractAlthough the basic taxonomic characteristics usually remain unchanged, some spinning apparatuses undergo consistent adaptive variations. As the presence of additional protuberances known as nubbins and tartipores have caused disagreements regarding some Araneidae spiders, more detailed definitions on the cuticular structures have recently been proposed. Reflecting this definition, microstructural organization of silk spinning apparatuses in the orb web spider Argiope bruennichi were reconsidered using field emission scanning electron microscopy. Among the seven kinds of functional spigots in females, it was revealed that two types (major ampullates and pyrifoms) are located on anterior spinnerets and another five types are distributed on median (minor ampullates, tubuliforms and aciniforms) or posterior (tubuliforms, flagelliforms, aggregates and aciniforms) spinnerets, respectively. In addition to functional spigots, cuticular remnants of the nubbins and the tartipores were found on the spinning fields, but the number of tartipores on each spinneret varied among individuals based on maturity. Nevertheless, three kinds of cuticular protuberances of ampullate silk glands were clearly visible at both the anterior and median spinnerets.

Developmental changes in spider spinning fields: a comparison between Mimetus and Araneus (Araneae: Mimetidae, Araneidae)

As part of an effort to understand the changes that piriform (Pi) and aciniform (Ac) silk glands undergo throughout the molt–intermolt cycle, spinnerets from all instars of two Mimetus Hentz, 1832 and one Araneus Clerck, 1757 species were examined by scanning electron microscopy. Especially informative were scans of spinning fields from the same individual over two or more consecutive stadia. These allowed us to determine that, in both genera, the Pi and Ac glands in use during a given stadium could be divided into two categories: (1) those with ducts accommodated by tartipores during proecdysis and (2) those not so accommodated and thereby apparently not functional during proecdysis. A silk gland in the former category, once developed, could presumably be used, at most, in every other stadium, whereas one of the latter category could potentially be used in every stadium. Unexpectedly, Pi glands of the latter category were constant in number [two per anterior lateral spinneret (ALS); four in total] throughout the ontogenies of both genera, and their spigots occupied the same location in the Pi spinning field in both genera. By contrast, tartipore-accommodated Pi glands increased in number from one stadium to the next in both genera. Of the Ac glands that had their spigots located on the posterior median spinnerets, none were tartipore-accommodated in either genera but, of the Ac glands with spigots on the posterior lateral spinnerets (PLS), some were tartipore-accommodated and some were not. All of them increased in number during the ontogenies of both genera. Adult males of three Mimetus species had two unusual spigots of unknown function on each ALS, which we interpret as modified Pi (MoPi) spigots. Their number and position raise the possibility that they serve (presumably modified) versions of the Pi glands that were not accommodated by tartipores during proecdysis. No spigots fully matching the description of Mimetus MoPi spigots were observed in adult males of four Australomimetus Heimer, 1986 or five Ero C. L. Koch, 1836 species. However, two of the Ero species did show a pair of Pi spigots on each ALS that, although not as conspicuous as Mimetus MoPi spigots, had wider openings than other Pi spigots. A minority of juvenile Mimetus specimens, and no adults, had a protuberance on one or both of their PLS, in a position similar to that of the aggregate (Ag)-flagelliform (Fl) spigot triad of araneoids, which may represent a phylogenetic vestige of a Fl or Ag spigot or one of their homologues. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 343–383.

Appendage patterning in the South American bird spider Acanthoscurria geniculata (Araneae: Mygalomorphae)

Pattern formation by the genes dachshund (dac), Distal-less (Dll), extradenticle (exd) and homothorax (hth) in spider appendages has been studied previously only in members of the higher spiders (Araneomorphae). In order to study the diversity and conservation of pattern formation in spiders as a whole, we studied homologs of these genes in embryos of the bird spider Acanthoscurria geniculata, which belongs to the Mygalomorphae, a more primitive spider group. We show that the patterns of dac and Dll are largely conserved in all spiders studied so far. We find a duplication of hth and exd genes as previously identified in the higher spider Cupiennius salei. These data suggest that pattern formation shows little diversity in all spiders, including the duplication of hth and exd that likely occurred before the split of Mygalomorphae and Araneomorphae. We also find that the legs and pedipalps bear endites of which only the pedipalpal endite expresses Dll and is retained in the adult. Similarly, the limb buds of the posterior spinnerets express Dll and become segmented appendages in the adult, whereas the anterior spinnerets lack Dll expression and are absent in postembryonic stages. In both cases, the expression of Dll or the lack of it indicates structures which will be retained as adult traits or rudimentary structures that degenerate, respectively. The presence of embryonic rudiments of leg endites in Acanthoscurria and the leg-like pattern formation in the posterior spinnerets are interpreted as primitive traits that have been lost in the Araneomorphae.

Silk spinning apparatuses in the cribellate spider nurscia albofasciata (Araneae: Titanoecidae)

The fine structural characteristics of the silk spinning apparatus in the titanoecid spiders Nurscia albofasciata have been examined by the field emission scanning electron microscopy (FESEM). This titanoecid spiders have a pair of medially divided cribella just in front of the anterior spinnerets, and the surface of the cribellum is covered by hundred of tiny spigots which produce numerous cribellate silk fibrils. The cribellar silks are produced from the spigots of the sieve‐like prate, and considered as a quite different sort of catching silk with dry‐adhesive properties. The other types of the silk spigots were identified as follows: ampullate, pyriform and aciniform glands. Two pairs of major ampullate glands send secretory ductules to the anterior spinnerets, and another 1–2 pairs of minor ampullate glands supply the middle spinnerets. In addition, the pyriform glands send ductules to the anterior spinnerets, and two kinds of the aciniform spigots feed silk into the middle (A type) and the posterior spinnerets (both of A & B types), respectively.

Microstructure of the silk apparatus in the coelotine spider Paracoelotes spinivulva (Araneae: Amaurobiidae)

AbstractThe microstructural characteristics of the silk‐spinning apparatus and its ecological significance in the coelotine spider Paracoelotes spinivulva were examined by field emission scanning electron microscopy, with the goal of understanding the properties and the evolutionary origins of these silk constructs. The silk apparatuses of this spider were composed of four basic types of silk‐spinning spigot (ampullate, pyriform, aciniform and tubuliform), which connected with typical silk glands in the abdominal cavity. Of the three pairs of spinnerets, the posterior pairs were highly elongated along the body axis. Anterior spinnerets comprised two pairs of ampullate glands and approximately 70–80 pairs of pyriform glands in both sexes. Middle spinnerets had one to two pairs of ampullate spigots, three pairs of tubuliform spigots in females, and 50–60 (female) or 80–90 (male) pairs of aciniform spigots. An additional two pairs of tubuliform spigots in females and 70–80 (female) or 100–120 (male) pairs of aciniform spigots were counted on the spinning surfaces of the posterior spinnerets in both sexes. Although the coelotine spiders use their silk to catch prey, P. spinivulva characteristically do not have a typical “triad” spigot, including a flagelliform and two aggregate spigots, for capture thread production.

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

AbstractThe genus Oxytate L. Koch, 1878 comprises a homogeneous group of nocturnal crab spiders that have silk apparatuses even though they do not spin webs to trap prey. We examined the microstructure of the silk spinning apparatus of the green crab spider Oxytate striatipes, using field emission scanning electron microscopy. The silk glands of the spider were classified into three types: ampullate, pyriform and aciniform. The spigots of these three types of silk gland occur in both sexes. Two pairs of major ampullate glands send secretory ductules to the anterior spinnerets, and another two pairs of minor ampullate glands supply the median spinnerets. In addition, the pyriform glands send ductules to the anterior spinnerets (45 pairs in females and 40 pairs in males), and the aciniform glands feed silk into the median (9–12 pairs in females and 7–10 pairs in males) and the posterior (30 pairs in both sexes) spinnerets. The spigot system of O. striatipes is simpler and more primitive than other wandering spiders: even the female spiders possess neither tubuliform glands for cocoon production nor triad spigots for web‐building.

Revision of the Australian wolf spider genus Anomalosa Roewer, 1960 (Araneae: Lycosidae)

The wolf spider genus Anomalosa Roewer, 1960 is revised with Anomalosa kochi (Simon, 1898) as type species. Anomalosa includes a further Australian species, A. oz sp. nov. Representatives of Anomalosa are small, elongated lycosids with a longitudinal light median band on the dorsal shield of the prosoma and on the opisthosoma, the latter being particularly distinct in males. They are closely related to Venonia Thorell, 1894. Similar to Venonia, males have a bipartite prolateral tegular lobe on the pedipalp, but it is much larger than in Venonia and, in contrast to Venonia, larger than the membranous tegular apophysis. Anomalosa kochi has only been found in Queensland, whereas the distribution of A. oz sp. nov. includes New South Wales, South Australia and Victoria. This allopatric distribution coincides with the McPherson Range as a biogeographical border. Although most males and females of Anomalosa have been caught in pitfall traps or running freely in moderately moist habitats, such as near creeks and dams, there is evidence that representatives of this genus build sheet-webs similar to Venonia. This behaviour is supported by morphological evidence as species of Anomalosa have elongated posterior spinnerets. The original description of A. harishi (Dyal, 1935) from Panjab, India, does not match the diagnosis of Anomalosa. Consequently, I reject the inclusion of A. harishi in Anomalosa and re-transfer it to its original genus Anomalomma Simon, 1890, Anomalomma harishi Dyal, 1935, pending a systematic revision of this genus.

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

AbstractThe 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).

Systematics and biogeography of the sheet-web building wolf spider genus Venonia (Araneae:Lycosidae)

The Australian/Oriental wolf spider genus Venonia Thorell, 1894 (type species V. coruscans Thorell, 1894) belongs to one of the few true web-building genera within the Lycosidae. Their small sheet-webs with funnel-like retreats are generally found in the ground layer of vegetation, such as on lawns and meadows, but also in depressions of soil and under roots of trees. Members of the genus Venonia are easily identified within the Lycosidae due to a unique combination of somatic and genitalic characters. Most conspicuous is a posterodorsal white spot on the abdomen just above the elongated posterior spinnerets on an otherwise uniformly coloured, small, and relatively slender spider. The cymbium of the male pedipalp is highly asymmetrical appearing retrolaterally truncated. Its tegular apophysis is membranous. The female epigyne is generally not sclerotised and has a posterior central incision. Our revision recognises fifteen species of which seven are new to science: V. chaiwooi, sp. nov.; V. choiae, sp. nov.; V. cinctipes (Simon, 1898); V. coruscans Thorell, 1894; V. infundibulum, sp. nov.; V. joejim, sp. nov.; V. kimjoopili, sp. nov.; V. kokoda Lehtinen & Hippa, 1979; V. micans (Simon, 1898) (= Venonia gabrielae Barrion & Litsinger, 1995, new synonymy); V. micarioides (L. Koch, 1877); V. milla Lehtinen & Hippa, 1979; V. muju (Chrysanthus, 1967); V. nata, sp. nov.; V. sungahae, sp. nov.; and V. vilkkii Lehtinen & Hippa, 1979. A phylogenetic analysis including representatives of the venoniine genera Anomalosa Roewer, 1960 and Allotrochosina Roewer, 1960 with Pirata subpiraticus (Bösenberg & Strand, 1906) as outgroup suggests a Gondwanan origin of the Venoniinae and one dispersal event within Venonia from the Australian region into Wallacea and only one dispersal event by V. coruscans into the Oriental region. Venonia spirocysta Chai, 1991 from China is not a true Venonia and is here considered incerta sedis. We reject the inclusion of the genus Zoica Simon, 1898 in the subfamily Venoniinae Lethinen & Hippa, 1979 due to considerable morphological differences in representatives of this genus (in particular in the male pedipalp), and therefore consider the subfamily Zoicinae Lehtinen & Hippa, 1979 as valid.

Microstructural Analysis of the Capture Thread Spinning Apparatus in Orb Web Spiders

ABSTRACTThe microstructural characteristics of the capture thread production from silk glands in the orb web spiders were analyzed using scanning and transmission electron microscopes. Sticky and gluey capture threads of the web are originated from the silks of two flagelliform glands and four aggregate glands. They supply precursors of the secretory silks to a pair of characteristic “triad” spinning units on the posterior spinnerets. The aggregate gland is composed of large and multi‐lobed secretory region and thick excretory duct surrounded by large irregular nodules. The excretory duct of this gland basically consists of three superposed types of cells which are inner columnar epithelium, nodule forming cells and outer connectives. The nodules contain numerous mitochondria and glycogen particles within their cytoplasm and they are surrounded by the same sheath of thin connective tissues. Secretory region of the aggregate gland which produce water‐soluble components of the capture thread comprises discrete secretory vesicles and extensive rough endoplasmic reticulum. Characteristically, secretory droplets are formed without involvement of the Golgi complexes, suggesting that they do not play an important role in the processing of the capture threads. However the electron densities and internal textures of the granules are observed with diverse according to their maturation level. Finally, the secretory products are released by the mechanism of apocrine secretion losing part of their cytoplasm during this process.

Spinneret Microstructure of the Silk Spinning Apparatus in the Crab Spider, Misumenops tricuspidatus (Araneae: Thomisidae)

ABSTRACTThe silk spinning apparatus in the crab spider, Misumenops tricuspidatus was studied with the field emission scanning electron microscope (FESEM) and the main microstructural characteristics of the silk glands are presented. In spite of the fact that the crab spiders do not spin webs to trap a prey, they also have silk apparatus even though the functions are not fully defined. The crab spider, Misumenops tricuspidatus possesses only three types of silk glands which connected through the typical spinning tubes on the spinnerets. The spinning apparatus of Misumenops closely corresponds to that of wandering spiders such as jumping spiders or wolf spiders except some local variations. Anterior spinnerets comprise 2 pairs of the ampullates and 48 (±5) pairs of pyriform glands. Another 2 pairs of ampullate glands and nearly 20 (±3) pairs of aciniform glands were connected on the middle spinnerets. Additional 50 (±5) pairs of the aciniform glands were connected on the posterior spinnerets. The aggregate glands and the flagelliform glands which have the function of sticky capture thread production in orb‐web spiders as well as the tubuliform glands for cocoon production in females were not developed at both sexes of this spider, characteristically.