Cribellum literally means "little sieve", and in biology the term generally applies to anatomical structures in the form of tiny perforated plates.
16-460: Crevice weaver spiders ( Filistatidae ) comprise cribellate spiders with features that have been regarded as " primitive " for araneomorph spiders. They are weavers of funnel or tube webs. The family contains 18 genera and more than 120 described species worldwide. One of the most abundant members of this family in the Americas is the southern house spider ( Kukulcania hibernalis ). Named after
32-561: A cribellum. The presence or absence of a cribellum is used to classify araneomorph spiders into the cribellate and ecribellate (not cribellate) type. The distinction can be used to study evolutionary relationships. However, in 1967 it was discovered that there are many families with both cribellate and ecribellate members ( Lehtinen , 1967). Some species, such as Amaurobius ferox , are also capable of switching between cribellate and ecribellate silk, primarily using cribellate silk for webs and ecribellate silk for trophic eggs. Today, it
48-554: A whole (such as an M-shaped midgut) could actually be novel derived features ( synapomorphies ) of the Hypochilidae-Filistatidae clade. As of April 2019, the World Spider Catalog accepts the following genera: Cribellate In certain groups of diatoms it refers to microscopically punctured regions of the frustule , or outer layer. In certain groups of spider species, so-called cribellate spiders,
64-443: A woolly texture. The fibers are so small in diameter that they are strongly subject to Van der Waals forces . In addition, the fibres have a surface that absorbs waxes from the epicuticle of insect prey on contact. This creates a powerful adhesion without any liquid glue that tends to dry out. The spider cribellum is a functional homolog of the anterior median spinnerets of Mesothelae and Mygalomorphae , which do not have
80-445: Is believed that the precursor of all Araneomorphae was cribellate ( symplesiomorphy ), and that this function was lost in some araneomorph spiders secondarily (Coddington & Levy, 1991). Many of these still retain a colulus , which is thought to be a reduced cribellum, and is of unknown function. However, some "ecribellate" spiders seem to have evolved independently, without cribellate precursors (Foelix, 1979). In Austrochilidae ,
96-445: The cribellum is a silk spinning organ. Unlike the usual spinnerets of spiders, the cribellum consists of one or more plates covered in thousands of tiny spigots , tiny holes that hardly project from the surface, in contrast to the elongated spigots that project from spinnerets. These minute spigots produce extremely fine fibers, merely tens of nanometres thick, which are combed out by the spider's calamistrum , producing silk with
112-399: The cribellum . The calamistrum and cribellum are used to form the hackled bands of silk which are characteristic of the webs of these spiders. The calamistrum is found on the upper margin of the metatarsus of the hind legs. Each bristle of the calamistrum is serrated on one side and smooth on the other. The length of a spider's calamistrum is always equal to or greater than the width of
128-412: The frustule , or outside layer of many forms of diatom also are called cribella. In such species of diatom the frustule consists of a thin siliceous plate with many small pores. Calamistrum In spiders , the calamistrum is a row of specialized leg bristles used to comb out fine bands of silk . It is only found on cribellate spiders, that is, spiders that possess the spinning organ known as
144-477: The cribellum is developed only in the second nymphal stage, so the ecribellate and cribellate conditions change during the spider ontogenesis . Only about 180 genera in 23 families (1991) still contain cribellate members, although the diverse Australian cribellate fauna is still mostly undescribed. However, that fauna may be an example of high diversity in Australian animals that are only relicts in other regions of
160-528: The family was described in 2014 as "one of the most enigmatic problems in spider phylogeny". A 2015 study, based on genomic data, places Filistatidae with Hypochilidae in a clade outside most of the families previously placed in Haplogynae: Hypochilidae Filistatidae most other "traditional" haplogynes Leptonetidae Entelegynae This placement suggests that features that were thought to be "primitive" to araneomorph spiders as
176-449: The fierce Meso-American god Kukulkan , the females are large (up to nearly 20 mm) dark-colored spiders and males are light brown, smaller (about 10 mm), but more long-legged and with palps that are held together in front of their carapaces like the horn of a unicorn . The males also have a darker streak on the center of the dorsal carapace that causes them to be often mistaken for brown recluse spiders . The tiny members of
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#1732886496024192-603: The genus Filistatinella are like miniature versions of Kukulcania . The nominate genus Filistata is Afro-Eurasian in distribution. In many older books the species from the Americas now placed in the genus Kukulcania are placed in Filistata . A striking visual characteristic of the family, beside dimorphism, is the unusual upward bend encountered near the femur of the first pair of legs. While resembling hydraulic muscle mechanisms akin to arthropods, this modification actually allows
208-427: The number of segments of the anterior lateral spinnerets. They have other features which have been regarded as "primitive": an M-shaped intestine, only leg IV moving while combing silk, and posterior book lung leaves being present in early juveniles. A 2013 study based on molecular evidence placed the family as sister to a clade consisting of Hypochilidae and the remaining haplogynes. The precise phylogenetic position of
224-455: The species he called Filistata bicolor (now Filistata insidiatrix ), a Mediterranean species also found in southern Austria. On the basis of the features of the male and female genitalia, the family was placed in the Haplogynae , usually as the sister taxon of the remaining members of the group. However, unlike the other haplogynes, Filistatidae are cribellate and do not show a decrease in
240-404: The spider to retain the prey directly from the crevice it occupies. Also, if the larger prey ever tries to pull it from the crevice, the spider can use these legs to "grab" to the side walls and hence make it difficult. Many Kukulcania species also use them to dig holes in the soft ground at a 25- to 30-degree angle. The family Filistatidae was created in 1867 by Anton Ausserer . It was based on
256-824: The world, like the marsupials (Coddington & Levy, 1991). Cribellate taxa are not very speciose, and for nearly all cribellate-ecribellate sister clades the cribellate lineage is less diverse (Coddington & Levy, 1991), for example: 22 families of araneomorph spiders, namely Agelenidae , Amaurobiidae , Amphinectidae , Austrochilidae , Ctenidae , Deinopidae , Desidae , Dictynidae , Eresidae , Filistatidae , Gradungulidae , Hypochilidae , Miturgidae , Neolanidae , Nicodamidae , Oecobiidae , Psechridae , Stiphidiidae , Tengellidae , Titanoecidae , Uloboridae and Zoropsidae contain at least some cribellate spiders (Griswold et al. 1999). While some of these families are entirely cribellate, others contain both cribellate and ecribellate species. The perforated regions of
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