Progradungula otwayensis immature male with catching ladder

Cribellum literally means "little sieve", and in biology the term generally applies to anatomical structures in the form of tiny perforated plates. In certain groups of

diatom A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...

s it refers to microscopically punctured regions of the frustule, or outer layer. In certain groups of spider species, so-called cribellate spiders, the cribellum is a

silk Silk is a natural fiber, natural protein fiber, some forms of which can be weaving, woven into textiles. The protein fiber of silk is composed mainly of fibroin and is most commonly produced by certain insect larvae to form cocoon (silk), c ...

spinning organ. Unlike the usual

spinnerets A spinneret is a silk-spinning organ of a spider or the larva of an insect. Some adult insects also have spinnerets, such as those borne on the forelegs of Embioptera. Spinnerets are usually on the underside of a spider's opisthosoma, and ar ...

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 In spiders, the calamistrum is a row of specialized leg bristles used to comb out fine bands of spider silk, silk. It is only found on cribellate spiders, that is, spiders that possess the spinning organ known as the cribellum. The calamistrum and ...

, producing silk with a woolly texture. The fibers are so small in diameter that they are strongly subject to

Van der Waals force In molecular physics and chemistry, the van der Waals force (sometimes van der Waals' force) is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical elec ...

s. In addition, the fibres have a surface that absorbs waxes from the

epicuticle Arthropods are covered with a tough, resilient integument, cuticle or exoskeleton of chitin. Generally the exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins. T ...

of insect prey on contact. This creates a powerful adhesion without any liquid glue that tends to dry out. Bott, Raya A. Baumgartner, Werner Bräunig, Peter Menzel, Florian Joel, Anna-Christin. Adhesion enhancement of cribellate capture threads by epicuticular waxes of the insect prey sheds new light on spider web evolution. Proceedings of the Royal Society B. 31 May 2017. The spider cribellum is a functional homolog of the anterior median spinnerets of

Mesothelae The Mesothelae are a suborder of spiders (order Araneae). , two extant families were accepted by the World Spider Catalog, Liphistiidae and Heptathelidae. Alternatively, the Heptathelidae can be treated as a subfamily of a more broadly circum ...

and

Mygalomorphae The Mygalomorphae, or mygalomorphs, are an infraorder of spiders, and comprise one of three major groups of living spiders with over 3,000 species, found on all continents except Antarctica. Many members are known as trapdoor spiders due to t ...

, which do not have a cribellum.

Ancestral trait

The presence or absence of a cribellum is used to classify

araneomorph The Araneomorphae (also called the Labidognatha or "true spiders") are an infraorder of spiders. They are distinguishable by chelicerae (fangs) that point diagonally forward and cross in a pinching action, in contrast to the Mygalomorphae (taran ...

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 ''Amaurobius ferox'', sometimes known as the black lace-weaver, is a common nocturnal spider belonging to the family Amaurobiidae and genus '' Amaurobius''. Its genus includes three subsocial species, ''A. fenestralis, A. similis'' and ''A. fer ...

'', are also capable of switching between cribellate and ecribellate silk, primarily using cribellate silk for webs and ecribellate silk for trophic eggs. Today, it is believed that the precursor of all

Araneomorphae The Araneomorphae (also called the Labidognatha or "true spiders") are an infraorder of spiders. They are distinguishable by chelicerae (fangs) that point diagonally forward and cross in a pinching action, in contrast to the Mygalomorphae (taran ...

was cribellate (

symplesiomorphy In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, an ...

), 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 Austrochilidae is a small spider family with nine species in two genera. ''Austrochilus'' and ''Thaida'' are endemic (ecology), endemic to the Andean forest of central and southern Chile and adjacent Argentina. Taxonomy , two genus, genera are p ...

, the cribellum is developed only in the second nymphal stage, so the ecribellate and cribellate conditions change during the spider

ontogenesis Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...

Prevalence

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 the world, like the

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

s (Coddington & Levy, 1991). Cribellate

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

are not very speciose, and for nearly all cribellate-ecribellate sister

clades In biology, a clade (), also known as a monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach to taxonomy ...

the cribellate lineage is less diverse (Coddington & Levy, 1991), for example: *

Haplogynae The Haplogynae or haplogynes are one of the two main groups into which araneomorph spiders have traditionally been divided, the other being the Entelegynae. Morphological phylogenetic studies suggested that the Haplogynae formed a clade; more re ...

: cribellate

Filistatidae 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 s ...

c. 100 species, all others (mostly ecribellate) c. 3,000 species *

Entelegynae The Entelegynae or entelegynes are a subgroup of araneomorph spiders, the largest of the two main groups into which the araneomorphs were traditionally divided. Females have a genital plate ( epigynum) and a "flow through" fertilization system; ...

: cribellate Deinopoidea c. 320 species, ecribellate

Araneoidea Araneoidea is a taxon of Araneomorphae, araneomorph spiders, termed "araneoids", treated as a Family (biology), superfamily. As with many such groups, its Circumscription (taxonomy), circumscription has varied; in particular some families that ha ...

c. 11,000 species

Cribellate families

22 families of

spiders, namely

Agelenidae The Agelenidae are a large family of spiders in the suborder Araneomorphae. Well-known examples include the common "grass spiders" of the genus ''Agelenopsis''. Nearly all Agelenidae are harmless to humans, but the bite of the hobo spider (''Era ...

Amaurobiidae Amaurobiidae is a family of three-clawed cribellate or ecribellate spiders found in crevices and hollows or under stones where they build retreats, and are often collected in pitfall traps. Unlidded burrows are sometimes quite obvious in crusty, ...

, Amphinectidae,

Ctenidae Wandering spiders (''Ctenidae'') are a family of spiders that includes the Brazilian wandering spiders. These spiders have a distinctive longitudinal groove on the top-rear of their oval carapace similar to those of the Amaurobiidae. They are h ...

Deinopidae Deinopidae, also known as net casting spiders, is a family of cribellate spiders first described by Carl Ludwig Koch in 1850. It consists of stick-like elongated spiders that catch prey by stretching a web across their front legs before propellin ...

Desidae Desidae is a family of spiders, some of which are known as intertidal spiders. The family is named for the genus '' Desis'', members of which inhabit the intertidal zone. The family has been reevaluated in recent years and now includes inland gen ...

Dictynidae Dictynidae is a family of cribellate, hackled band-producing spiders first described by Octavius Pickard-Cambridge in 1871. Most build irregular webs on or near the ground, creating a tangle of silken fibers among several branches or stems of on ...

, Eresidae,

Gradungulidae Gradungulidae, also known as large-clawed spiders, is a spider family endemic to Australia and New Zealand. They are medium to large-sized haplogyne spiders with three claws and two pairs of book-lungs similar to Mygalomorphae. Some species buil ...

Hypochilidae Lampshade spiders, family Hypochilidae, are among the most primitive of araneomorph spiders. There are two genus, genera and twelve species currently recognized. Like mygalomorphs, most hypochilids have two pairs of book lungs, but like araneomor ...

Miturgidae Miturgidae is a family of araneomorph spiders that includes nearly 170 species in 29 genera worldwide. First described by Eugène Simon in 1886, it has been substantially revised, and includes the previous family Zoridae as a synonym, and exclude ...

, Neolanidae,

Nicodamidae Nicodamidae is a family of Araneomorphae, araneomorph spiders with twenty-seven species in seven genera. They are small to medium-sized spiders found near the ground of eucalypt forest in small sheet webs. The species of this family are only prese ...

Oecobiidae Oecobiidae, also called disc web spiders, is a family of Araneomorphae, araneomorph spiders, including about 100 described species. They are small to moderate sized spiders, about long combined head and body length, depending on the species. Lar ...

, Psechridae,

Stiphidiidae Stiphidiidae, also called sheetweb spiders, is a family of araneomorph spiders first described in 1917. Most species are medium size ('' Stiphidion facetum'' is about long) and speckled brown with long legs. All members of this family occur in ...

, Tengellidae,

Titanoecidae Titanoecidae is a family of araneomorph spiders first described by Pekka T. Lehtinen in 1967. It is fairly widespread in the New World and Eurasia with five genera and more than 50 species worldwide. These are mostly dark-colored builders of "wool ...

Uloboridae Uloboridae is a family of non- venomous spiders, known as cribellate orb weavers or hackled orb weavers. Their lack of venom glands is a secondarily evolved trait. Instead, they wrap their prey thoroughly in silk, cover it in regurgitated digestiv ...

and

Zoropsidae Zoropsidae, also known as false wolf spiders for their physical similarity to wolf spiders, is a family of cribellate araneomorph spiders first described by Philipp Bertkau in 1882. They can be distinguished from wolf spiders by their two row ...

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.

Diatom cribellum

The perforated regions of the frustule, or outside layer of many forms of

also are called cribella. In such species of diatom the frustule consists of a thin siliceous plate with many small pores.

References

* Lehtinen, P.T. (1967). Classification of the Cribellate spiders and some allied families, with notes on the evolution of the suborder Araneomorpha. ''Ann. Zool. Fennici'' 4: 199–467. * Foelix, Rainer F. (1979). Biologie der Spinnen. Georg Thieme Verlag Stuttgart. * Coddington, J.A. & Levi, H.W. (1991). Systematics and Evolution of Spiders (Araneae). ''Annu. Rev. Ecol. Syst.'' 22: 565–592. * Eberhard, William G. and Pereira, Flory. (1993). Ultrastructure of cribellate silk of nine species in eight families and possible taxonomic implications (Araneae: Amaurobiidae, Deinopidae, Desidae, Dictynidae, Filistatidae, Hypochilidae, Stiphidiidae, Tengellidae). ''Journal of Arachnology'' 21(3): 161–174
PDF
* Huber, B.A. (1994): Spermophore morphology reveals a new synapomorphy of ''Oecobius'' and ''Uroctea'' (Araneae, Oecobiidae). ''Journal of Arachnology'' 22: 73–74
PDF
* Griswold, C.E., Coddington, J.A., Platnick, N.I. and Forster, R.R. (1999). Towards a Phylogeny of Entelegyne Spiders (Araneae, Araneomorphae, Entelegynae). ''Journal of Arachnology'' 27: 53–63
PDF

External links

(description and pictures)

{{Spider nav Spider anatomy