Cribellum
Encyclopedia
The cribellum is a silk
spinning organ found in certain spider
s. Unlike normal spinnerets, the cribellum consists of one or more plates covered in thousands of tiny spigots. These spigots produce extremely fine fibers which are combed out by the spider's calamistrum
, producing silk with a wooly texture. The fibers are so small in diameter that prey insects easily become entangled in them, without any glue
needed. The spiders then bite them before they can get away.
The cribellum is a functional homolog of the anterior median spinnerets of Mesothelae
and Mygalomorphae
, which do not have 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 found out that there are many families with both cribellate and ecribellate members (Lehtinen, 1967). It is today 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).
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
s (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:
spiders (Agelenidae, Amaurobiidae, Amphinectidae
, Austrochilidae
, Ctenidae, Deinopidae
, Desidae, Dictynidae, Eresidae, Filistatidae, Gradungulidae
, Hypochilidae, Miturgidae, Neolanidae, Nicodamidae
, Oecobiidae
, Psechridae
, Stiphidiidae
, Tengellidae, Titanoecidae, Uloboridae, 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.
is also called a cribellum. It consists of a thin siliceous membrane covered with small pores.
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...
spinning organ found in certain spider
Spider
Spiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
s. Unlike normal spinnerets, the cribellum consists of one or more plates covered in thousands of tiny spigots. These spigots produce extremely fine fibers which are combed out by the spider's calamistrum
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 the cribellum. The calamistrum and cribellum are used to form the hackled bands of silk which are...
, producing silk with a wooly texture. The fibers are so small in diameter that prey insects easily become entangled in them, without any glue
Glue
This is a list of various types of glue. Historically, the term "glue" only referred to protein colloids prepared from animal flesh. The meaning has been extended to refer to any fluid adhesive....
needed. The spiders then bite them before they can get away.
The cribellum is a functional homolog of the anterior median spinnerets of Mesothelae
Mesothelae
The Mesothelae are a suborder of spiders that includes the extinct families Arthrolycosidae and Arthromygalidae and the only extant family Liphistiidae....
and Mygalomorphae
Mygalomorphae
The Mygalomorphae, , are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other .-Description:...
, which do not have a cribellum.
The presence or absence of a cribellum is used to classify araneomorph
Araneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...
spiders into the cribellate and ecribellate (not cribellate) type. The distinction can be used to study evolutionary relationships. However, in 1967 it was found out that there are many families with both cribellate and ecribellate members (Lehtinen, 1967). It is today believed that the precursor of all Araneomorphae was cribellate (symplesiomorphy
Symplesiomorphy
In cladistics, a symplesiomorphy or symplesiomorphic character is a trait which is shared between two or more taxa, but which is also shared with other taxa which have an earlier last common ancestor with the taxa under consideration...
), 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).
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
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
s (Coddington & Levy, 1991).
Cribellate taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
are not very speciose, and for nearly all cribellate-ecribellate sister clades the cribellate lineage is less diverse (Coddington & Levy, 1991), for example:
- HaplogynaeHaplogynaeThe Haplogynae are a series of araneomorph spiders.Unlike the Entelegynae, they lack hardened female genitalia .Most of the species within this group have six eyes, as opposed to most other spiders...
: cribellate Filistatidae ca. 100 species, all others (mostly ecribellate): ca. 3,000 species - UloboroideaUloboroideaThe Uloboroidea are a superfamily of cribellate araneomorph spiders. They contain two families of eight-eyed spiders:* Deinopidae* Uloboridae...
ca. 320 species, AraneoideaAraneoideaThe Araneoidea are a superfamily of araneomorph spiders. They contain families of eight-eyed spiders:* Anapidae* Araneidae* Cyatholipidae* Linyphiidae* Mysmenidae* Nephilidae* Nesticidae* Pimoidae* Sinopimoidae* Symphytognathidae* Synaphridae...
: ca. 11,000 species
Cribellate families
22 families of araneomorphAraneomorphae
The Araneomorphae are a suborder of spiders. They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae , which have fangs that are nearly parallel in alignment.- Distinguishing characteristics :Note the difference in the...
spiders (Agelenidae, Amaurobiidae, Amphinectidae
Amphinectidae
The Amphinectidae are a spider family with about 180 described species in 35 genera.The family Neolanidae, with its only genus Neolana, was merged into this family in 2005.-Distribution:...
, Austrochilidae
Austrochilidae
The Austrochilidae are a small spider family with nine species in three genera.Two genera are endemic to the Andean forests of central and southern Chile and adjacent Argentina, the third is endemic to Tasmania.-Species:...
, Ctenidae, Deinopidae
Deinopidae
The spider family Deinopidae consists of stick-like elongate spiders that build unusual webs that they suspend between the front legs. When prey approaches, the spider will stretch the net to two or three times its relaxed size and propel itself onto the prey, entangling it in the web...
, Desidae, Dictynidae, Eresidae, Filistatidae, Gradungulidae
Gradungulidae
The Gradungulidae are a small spider family of Australia and New Zealand with 16 species in seven genera. They are medium to large three-clawed haplogyne spiders with two pairs of book-lungs ....
, Hypochilidae, Miturgidae, Neolanidae, Nicodamidae
Nicodamidae
The Nicodamidae are a spider family with 29 species in nine genera.They are small to medium sized spiders found in small sheet webs close to the ground in eucalypt forests...
, Oecobiidae
Oecobiidae
The spider family Oecobiidae consists of about 100 species.They are rather small ; some of them build tiny webs close to the ceiling in people's homes...
, Psechridae
Psechridae
The Psechridae are a family of spiders with about two dozen species in two living genera.They construct cribellate webs and are related to the Lycosidae. With body lengths of up to 2 cm and funnel webs more than 1 m in diameter, they are the biggest cribellate spiders. Psechrus species have been...
, Stiphidiidae
Stiphidiidae
The Stiphidiidae are a spider family with 94 described species in 13 genera. They are generally of medium size and build a horizontal tent-like web under rocks. Most species are speckled brown with long legs....
, Tengellidae, Titanoecidae, Uloboridae, 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.
Diatom cribellum
The outside layer of a diatomDiatom
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...
is also called a cribellum. It consists of a thin siliceous membrane covered with small pores.
External links
- The Spider - Web and Silk (description and pictures)
- Cribellate silk vs. sticky silk
- The Evolution of Web Usage in Spiders