Cribellum literally means "little sieve", and in biology the term generally applies to anatomical structures in the form of tiny perforated plates.
41-436: Caponiidae is a family of ecribellate haplogyne spiders that are unusual in a number of ways. They differ from other spiders in lacking book lungs and having the posterior median spinnerets anteriorly displaced to form a transverse row with the anterior lateral spinnerets. Most species have only two eyes, which is also unusual among spiders. A few species of Caponiidae variously have four, six or eight eyes. In some species
82-479: A complex development cycle of metamorphosis in which young animals may be totally different from older phases, such as the nauplius larvae of crustaceans, the nymphs of say, the Odonata , or the larvae of Endopterygota , such as maggots of flies. Such larval stages commonly have ecological and life cycle roles totally different from those of the mature animals. Secondly, often a major injury in one phase, such as
123-659: A sister group of the Tetrablemmidae plus the four families inside the superfamily Dysderoidea . The subfamily Nopinae consists at least of the genera Nops , Nopsides , Orthonops and Tarsonops . The remaining genera are unlikely to form a monophyletic group. The family is found in Africa and the Americas from Argentina to the United States. Calponia is a contraction of Californian Caponia , because
164-502: Is a component of a complex matrix of materials. It practically always is associated with protein molecules that often are in a more or less sclerotised state, stiffened or hardened by cross-linking and by linkage to other molecules in the matrix. In some groups of animals, most conspicuously the Crustacea , the matrix is greatly enriched with, or even dominated by, hard minerals, usually calcite or similar carbonates that form much of
205-400: Is a laminated structure of layers of interwoven fibrous chitin and protein molecules, while the exocuticle is the layer in which any major thickening, armouring and biomineralization occurs. Biomineralization with calcite is particularly common in Crustacea , whereas sclerotization particularly occurs in insects . The exocuticle is greatly reduced in many soft-bodied insects, especially in
246-405: Is a multi-layered structure with four functional regions: epicuticle , procuticle , epidermis and basement membrane . Of these, the epicuticle is a multi-layered external barrier that, especially in terrestrial arthropods, acts as a barrier against desiccation . The strength of the exoskeleton is provided by the underlying procuticle , which is in turn secreted by the epithelial cells in
287-445: 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 ,
328-446: Is called the sternum , which commonly bears sternites . The two lateral regions are called the pleura (singular pleurum) and any sclerites they bear are called pleurites. The arthropod exoskeleton is divided into different functional units, each comprising a series of grouped segments; such a group is called a tagma , and the tagmata are adapted to different functions in a given arthropod body. For example, tagmata of insects include
369-429: Is liable to failure under compression. This combination is especially effective in resisting predation, as predators tend to exert compression on the outer layer, and tension on the inner. Its degree of sclerotisation or mineralisation determines how the cuticle responds to deformation . Below a certain degree of deformation changes of shape or dimension of the cuticle are elastic and the original shape returns after
410-470: Is named in honor of one of the collectors, P.A. Goloboff. As of April 2019, the World Spider Catalog accepts the following genera: Ecribellate 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, the cribellum is a silk spinning organ. Unlike
451-405: Is periodic and concentrated into a period of time when the exoskeleton is shed, called moulting or ecdysis , which is under the control of a hormone called ecdysone . Moulting is a complex process that is invariably dangerous for the arthropod involved. Before the old exoskeleton is shed, the cuticle separates from the epidermis through a process called apolysis . Early in the process of apolysis
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#1732780945692492-406: Is reinforced or stiffened by materials such as minerals or hardened proteins. This happens in parts of the body where there is a need for rigidity or elasticity. Typically the mineral crystals, mainly calcium carbonate , are deposited among the chitin and protein molecules in a process called biomineralization . The crystals and fibres interpenetrate and reinforce each other, the minerals supplying
533-430: Is used to refer to those parts of an insect's body lacking in setae (bristles) or scales . Chemically, chitin is a long-chain polymer of a N-acetylglucosamine , which is a derivative of glucose. The polymer bonds between the glucose units are β(1→4) links, the same as in cellulose . In its unmodified form, chitin is translucent, pliable, resilient and tough. In arthropods and other organisms however, it generally
574-460: 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
615-419: The exoskeleton . In some organisms the mineral content may exceed 95%. The role of the chitin and proteins in such structures is more than just holding the crystals together; the crystal structure itself is so affected as to prevent the propagation of cracks under stress, leading to remarkable strength. The process of formation of such mineral-rich matrices is called biomineralization . The difference between
656-405: 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. Arthropod cuticle#Morphology Arthropods are covered with a tough, resilient integument , cuticle or exoskeleton of chitin . Generally the exoskeleton will have thickened areas in which the chitin
697-429: The larval stages such as caterpillars and the larvae of parasitoidal Hymenoptera . In addition to the chitinous-proteinaceous composite of the cuticle, many crustaceans , some myriapods and the extinct trilobites further impregnate the cuticle with mineral salts, above all calcium carbonate, which can make up to 40% of the cuticle. The armoured product commonly has great mechanical strength. The two layers of
738-464: The anterior middle of the carapace. Caponiidae are unusual in the degree to which the eye number varies. In this they surpass even the family Cybaeidae in which some species have two eyes, some six, and some eight. In some species of the Caponiidae paired eyes meet in the midline, giving the spider in effect, an odd number of eyes. The following genera have eyes as follows: Their habits are for
779-483: 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
820-422: The cuticle have different properties. The outer layer is where most of the thickening, biomineralization and sclerotisation takes place, and its material tends to be strong under compressive stresses , though weaker under tension. When a rigid region fails under stress , it does so by cracking. The inner layer is not as highly sclerotised, and is correspondingly softer but tougher; it resists tensile stresses but
861-435: The cuticle then takes place. The new integument still is soft and usually is pale, and it is said to be teneral or callow . It then undergoes a hardening and pigmentation process that might take anything from several minutes to several days, depending on the nature of the animal and the circumstances. Although the process of ecdysis is metabolically risky and expensive, it does have some advantages. For one thing it permits
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#1732780945692902-439: The epidermis, which begins as a tough, flexible layer of chitin . Arthropod cuticle is a biological composite material , consisting of two main portions: fibrous chains of alpha- chitin within a matrix of silk-like and globular proteins, of which the best-known is the rubbery protein called resilin . The relative abundance of these two main components varies from approximately 50/50 to 80/20 chitin protein, with softer parts of
943-441: The epithelial cells release enzymatic moulting fluid between the old cuticle and the epidermis. The enzymes partly digest the endocuticle and the epidermis absorbs the digested material for the animal to assimilate. Much of that digested material is re-used to build the new cuticle. Once the new cuticle has formed sufficiently, the animal splits the remaining parts of the old integument along built-in lines of weakness and sheds them in
984-409: The exoskeleton are called sclerites. Sclerites may be simple protective armour, but also may form mechanical components of the exoskeleton , such as in the legs, joints, fins or wings. In the typical body segment of an insect or many other Arthropoda, there are four principal regions. The dorsal region is the tergum ; if the tergum bears any sclerites, those are called tergites . The ventral region
1025-426: The exoskeleton having a higher proportion of chitin. The cuticle is soft when first secreted, but it soon hardens as required, in a process of sclerotization . The process is poorly understood, but it involves forms of tanning in which phenolic chemicals crosslink protein molecules or anchor them to surrounding molecules such as chitins. Part of the effect is to make the tanned material hydrophobic . By varying
1066-415: 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 a cribellum. The presence or absence of a cribellum is used to classify araneomorph spiders into
1107-404: The hardened plates or sclerites of a typical body segment. In either case, in contrast to the carapace of a tortoise or the cranium of a vertebrate, the exoskeleton has little ability to grow or change its form once it has matured. Except in special cases, whenever the animal needs to grow, it moults, shedding the old skin after growing a new skin from beneath. A typical arthropod exoskeleton
1148-411: The hardness and resistance to compression, while the chitin supplies the tensile strength. Biomineralization occurs mainly in crustaceans. In insects and arachnids , the main reinforcing materials are various proteins hardened by linking the fibres in processes called sclerotisation and the hardened proteins are called sclerotin . The dorsal tergum , ventral sternum , and the lateral pleura form
1189-472: The head, which is a fused capsule, the thorax as nearly a fixed capsule, and the abdomen usually divided into a series of articulating segments. Each segment has sclerites according to its requirements for external rigidity; for example, in the larva of some flies, there are none at all and the exoskeleton is effectively all membranous ; the abdomen of an adult fly is covered with light sclerites connected by joints of membranous cuticle. In some beetles most of
1230-406: The integument of a heavily armoured crab, in which there is a very high degree of modification by biomineralization. The chemical and physical nature of the arthropod exoskeleton limits its ability to stretch or change shape as the animal grows. In some special cases, such as the abdomens of termite queens and honeypot ants means that continuous growth of arthropods is not possible. Therefore, growth
1271-486: The joints are so tightly connected, that the body is practically in an armoured, rigid box. However, in most Arthropoda the bodily tagmata are so connected and jointed with flexible cuticle and muscles that they have at least some freedom of movement, and many such animals, such as the Chilopoda or the larvae of mosquitoes are very mobile indeed. In addition, the limbs of arthropods are jointed, so characteristically that
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1312-406: The most part unknown. At least some species are known to hunt other spiders. The fact that they are ecribellate and haplogyne suggests that they might be relatively primitive . Calponia harrisonfordi from California seems to be the most primitive member of the family. Their phylogenetic relationships have long been enigmatic, but in the early 1990s it was determined that they are probably
1353-422: The number of eyes will increase when the spiderling changes its skin as it grows towards adulthood. These spiders of about 2 to 5 millimetres (0.079 to 0.197 in) are rarely noticed, but generally look like somewhat faded woodlouse hunter spiders in the genus Dysdera . The carapace (cephalothorax or prosoma) is orange and the abdomen (opisthosoma) light gray. The two-eyed species have their two eyes in
1394-785: The single species Calponia harrisonfordi has, like the African genus Caponia eight eyes. The species name is in honor of Harrison Ford , recognizing his efforts on behalf of the American Museum of Natural History . The Chilean caponiid fauna differs from that of the rest of the Neotropics in lacking members of the Nopinae (named after the genus Nops ). Three genera newly described by Norman I. Platnick in 1994 were thus named Notnops , Taintnops and Tisentnops , emphasizing this fact. The only Taintnops species, T. goloboffi ,
1435-401: The stress is removed. Beyond that level of deformation, non-reversible, plastic deformation occurs until finally the cuticle cracks or splits. Generally, the less sclerotised the cuticle, the greater the deformation required to damage the cuticle irreversibly. On the other hand, the more heavily the cuticle is armoured, the greater the stress required to deform it harmfully. Hardened plates in
1476-468: The types of interaction between the proteins and chitins, the insect metabolism produces regions of exoskeleton that differ in their wet and dry behaviour, their colour and their mechanical properties. The chitinous procuticle is formed of an outer exocuticle and the inner endocuticle , and between the exocuticle and endocuticle there may be another layer called mesocuticle which has distinctive staining properties. The tough and flexible endocuticle
1517-443: The unmodified and modified forms of chitinous arthropodan exoskeletons can be seen by comparing the body wall of say a bee larva, in which modification is minimal, to any armoured species of beetle , or the fangs of a spider. In both those examples there is heavy modification by sclerotisation. Again, contrasting strongly with both unmodified organic material such as largely pure chitin, and with sclerotised chitin and proteins, consider
1558-522: 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 a woolly texture. The fibers are so small in diameter that they are strongly subject to Van der Waals forces . In addition,
1599-400: The very name "Arthropoda" literally means "jointed legs" in reflection of the fact. The internal surface of the exoskeleton is often infolded, forming a set of structures called apodemes that serve for the attachment of muscles, and functionally amounting to endoskeletal components. They are highly complex in some groups, particularly in Crustacea . Within entomology , the term glabrous
1640-430: The visible process of ecdysis, generally shedding and discarding the epicuticle and the reduced exocuticle, though some species carry them along for camouflage or protection. The shed portions are called the exuviae . After the old cuticle is shed, the arthropod typically pumps up its body (for example, by air or water intake) to allow the new cuticle to expand to a larger size: the process of hardening by dehydration of
1681-824: 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