A cribellum is a kind of comb-like device in certain spiders, used to separate fibers of silk drawn from its spinnerets into many extremely fine fibers, giving it a wooly structure. Spiders are Predatory Invertebrate Animals that have two body segments, eight legs no chewing mouth parts and no wings Silk is a natural Protein Fiber, some forms of which can be woven into Textiles The best-known type of silk is obtained from cocoons A spinneret is a spider's silk -spinning organ. It is usually on the underside of a spider's Abdomen, to the rear Wool is the fiber derived from the specialized skin cells called follicles of animals in the Caprinae family principally sheep, but the hair of certain species Those fibers are so small in diameter that prey insects easily become entangled in them, without any glue needed. Glue or adhesive is a compound that adheres or bonds two items together The spiders then bite them before they can get away.

A cribellum is also a portion of diatom exoskeleton. Diatoms ( Greek: (dia = "through" + (temnein = "to cut" i An exoskeleton is an external Skeleton that supports and protects an animal's body in contrast to the internal Endoskeleton of for example a Human.

The cribellum is a functional homolog of the antorior median spinnerets of Mesothelae and Mygalomorphae, which do not have a cribellum. The Mesothelae are a suborder of Spiders (Order Araneae that includes the extinct families Arthrolycosidae and Arthromygalidae and the only Extant The Mygalomorphae, (also called the Orthognatha) are an Infraorder of Spiders The latter name comes from the orientation of the fangs which

The presence or absence of a cribellum is used to classify araneomorph spiders into the cribellate and ecribellate (not cribellate) type. The Araneomorphae are a Suborder of Spiders They are distinguished by having Chelicerae (fangs that point diagonally forward and cross in a pinching action 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). A symplesiomorphy or symplesiomorphic character is in Cladistics a trait which is shared (a symmorphy between two or more taxa, but which is also shared 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 marsupials (Coddington & Levy, 1991). Marsupials are an Infraclass of Mammals characterized by a distinctive pouch (called the marsupium) in which females carry their young through

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:

• Haplogynae: cribellate Filistatidae ca. A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor The Haplogynae are a series of araneomorph spiders Unlike the Entelegynae, they lack hardened (sclerotized female genitalia ( Epigynes The crevice weaver spiders (super-family Filistatoidea, family Filistatidae) contain primitive Cribellate, Haplogyne, weavers 100 species, all others (mostly ecribellate): ca. 3,000 species
• Uloboroidea ca. The Uloboroidea are a Superfamily of Cribellate araneomorph spiders 320 species, Araneoidea: ca. The Araneoidea are a Superfamily of araneomorph spiders They contain families of eight-eyed spiders Anapidae 11,000 species

Cribellate families

22 families of araneomorph 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. The Araneomorphae are a Suborder of Spiders They are distinguished by having Chelicerae (fangs that point diagonally forward and cross in a pinching action The Araneomorph funnel-web spiders of the family Agelenidae include the common grass spiders of the genus Agelenopsis, as well as the purportedly venomous Amaurobiidae is a family of spiders also known as "tangled nest Spiders quot "night spiders" or "hacklemesh weavers" The Amphinectidae are a Spider family with about 180 described species in 35 genera The Austrochilidae) are a small Spider family with nine species in three genera The wandering spiders is a term used to refer to the spider family Ctenidae The Spider family Deinopidae consists of stick-like elongate spiders that build unusual webs that they suspend between the front legs The intertidal spiders (family Desidae) live in a very unusual location — between the Tides Once thought to be limited to the Southern Hemisphere Dictynidae is a family of Cribellate (hackled band-producing Spiders Most spiders in this family build irregular webs close to or directly on the The velvet spiders (family Eresidae) are a small group (about 100 Species in 10 genera) of almost totally Old World spiders (exception a few species The crevice weaver spiders (super-family Filistatoidea, family Filistatidae) contain primitive Cribellate, Haplogyne, weavers The Gradungulidae are a small Spider family with 16 species in seven genera The Lampshade spiders of the family Hypochilidae are among the most primitive of Araneomorph Spiders There are two genera and eleven The long-legged sac spiders ( family Miturgidae) include nearly 400 Species in about 30 genera worldwide The Amphinectidae are a Spider family with about 180 described species in 35 genera The Nicodamidae are a Spider family with 29 species in nine genera The Spider family Oecobiidae (also called Disc web spiders) consists of about 100 species The Psechridae are a family of Spiders with about two dozen species in two orders The Stiphidiidae are a Spider family with 94 described species in 13 genera The tengellid spiders (family Tengellidae) include eight genera and a little over 30 Species worldwide The titanoecid spiders (family Titanoecidae) include only five genera and a little over 46 Species worldwide The hackled orbweavers (family Uloboridae) have the special distinction of being non- venomous Spiders Their lack of poison glands is a secondary evolved Zoropsidae is a family of uncommon somewhat Wolf spider -like wandering cribellate Spiders The eye arrangement is not like that of wolf 1999). While some of these families are entirely cribellate, others contain both cribellate and ecribellate species.

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. ISBN 313575801x
• 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

• The Spider - Web and Silk (description and pictures)
• Cribellate silk vs. sticky silk
• The Evolution of Web Usage in Spiders

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