Ecology of the true spiders (Araneomorphae) . Turnbull, A.L.. Access the full text: NOT AVAILABLE. Lookup the document at: google-logo. Ecology of the. Read “Ecology of the True Spiders (Araneomorphae), Annual Review of Entomology” on DeepDyve, the largest online rental service for. Turnbull, A.C. () Ecology of the True Spiders (Araneomorphae). Annual Review of Entomology, 18,
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Spiders order Araneae are air-breathing arthropods that have eight legs and chelicerae with fangs able to inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other orders of organisms.
Spider – Wikipedia
Anatomically, spiders differ from other arthropods in that the usual body segments are fused into two tagmatathe cephalothorax and abdomenand joined by a small, cylindrical pedicel. Th insectsspiders do not have antennae. In all except the most apiders group, the Mesothelaespiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in o cephalothorax.
Unlike most arthropods, spiders have no ecologgy muscles in their limbs and instead extend them by hydraulic pressure. Their abdomens bear appendages that have been modified into spinnerets that extrude silk from up to six types of glands. Spider webs vary widely in size, shape and the amount of sticky thread used.
It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse sspiders orb-web spiders. The species Bagheera kiplingi was described as herbivorous in but all other known species are predatorsmostly preying on insects and on other spiders, although a few large species zraneomorphae take birds and lizards.
It is estimated that the world’s 25 million tons of spiders kill — million tons of prey per year. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the genus Portia show signs of intelligence in their choice of tactics and ability to develop new ones.
Spiders’ guts are spiderw narrow to take solids, so they liquefy their food by flooding it with digestive enzymes. They also grind food with the bases of their pedipalpsas arachnids do not have the mandibles that crustaceans and insects have. To avoid being eaten by the females, which are typically much larger, male spiders identify themselves to potential mates by a variety of complex courtship rituals. Males of most species survive a few matings, limited mainly by their short life spans.
Females weave silk egg-cases, each of which may contain hundreds of eggs.
Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50, individuals.
Social behavior ranges from precarious toleration, as in the widow spidersto co-operative hunting and food-sharing. While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting pesticides. Spider silk provides a combination of lightness, strength and elasticity that is superior to that of synthetic materials, and spider silk genes have been inserted into mammals and plants to see if these can be used as silk factories.
As a result of their wide range of behaviors, spiders have become common symbols in art and mythology symbolizing various combinations of patience, cruelty and creative powers.
An abnormal fear of spiders is called arachnophobia. Spiders are chelicerates and therefore arthropods.
Ecology of the true spiders (Araneomorphae) 
In fact, chelicerates’ only appendages ahead of the mouth are a pair of cheliceraeand they lack anything that would function directly as “jaws”. Spiders and scorpions are members of one chelicerate group, the arachnids. The upper sections generally have thick “beards” that filter solid lumps out of their food, as spiders can take only liquid food.
In spiders, the cephalothorax and abdomen are joined by a small, cylindrical pedicelwhich enables the abdomen to move independently when producing silk. The upper surface of the cephalothorax is covered by a single, convex carapacewhile the underside is covered by two rather flat plates. The abdomen is soft and egg-shaped.
It shows no sign of spieers, except that the primitive Mesothelaewhose living members are the Liphistiidaercology segmented plates on the upper surface. Like other arthropods, spiders are coelomates in which the coelom is reduced to small areas round the reproductive and excretory systems.
Its place is largely taken by a hemocoela cavity that runs most of the length of the body and through which blood flows. The heart is a tube in the upper part of the body, with a few ostia that act as non-return valves allowing blood to enter the heart from the hemocoel but prevent it from leaving before it reaches the front end.
Hence spiders have open circulatory systems. Spiders have developed several different respiratory anatomies, based on book lungsa tracheal system, or both.
Mygalomorph and Mesothelae spiders have two pairs of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allow air to enter and diffuse oxygen. This is also the case for some basal araneomorph spiders, like the family Hypochilidaebut the remaining members of this group have just the anterior pair of araneomorpae lungs intact while the posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs.
Uniquely among cheliceratesthe final sections of spiders’ chelicerae are fangs, and the great majority of spiders can use truue to inject venom into prey from araneomorphhae glands in the roots of the chelicerae.
Some pump digestive enzymes from the midgut into the prey and then suck the liquified tissues of the prey into the gut, eventually leaving behind the empty husk of the prey. Others grind the prey to pulp using the chelicerae and the bases of the pedipalpswhile flooding it with enzymes; in these species, the chelicerae and the bases of the pedipalps form a preoral cavity that holds the food they are processing.
The stomach in the cephalothorax acts as a pump that sends the food deeper into the digestive system. The mid gut bears many digestive cecacompartments with no other exit, that extract nutrients from the food; most are in the abdomen, which is dominated by the digestive system, but a few are found in the cephalothorax. Most spiders convert nitrogenous waste products into uric acidwhich can be excreted as a dry material.
Malphigian tubules “little tubes” extract these wastes from the blood in the hemocoel and dump them into the cloacal chamber, from which they are expelled through the anus.
The basic arthropod central nervous system consists of a pair of nerve cords running below the gut, with paired ganglia as local control centers in all segments; a brain formed by fusion of the ganglia for the head segments ahead of and behind the mouth, so that the esophagus is encircled by this conglomeration of ganglia.
Despite the relatively small central nervous system, some spiders like Portia exhibit complex behaviour, including the ability to use a trial-and-error approach. Spiders have primarily four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another.
However, in spiders these eyes are capable of forming images. Unlike the principal eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum lucidumand wolf spiders can be spotted by torch light reflected from the tapeta.
On the other hand, jumping spiders’ secondary eyes have no tapeta. Other differences between the principal and secondary eyes are that the latter have rhabdomeres that point away from incoming light, just like in vertebrates, while the arrangement is the opposite in the former.
The principal eyes are also the only ones with eye muscles, allowing them to move the retina. Having no muscles, the secondary eyes are immobile.
Some jumping spiders’ visual acuity exceeds by a factor of ten that of dragonflieswhich have by far the best vision among insects ; in fact the human eye is only about five times sharper than a jumping spider’s.
They achieve this by a telephoto -like series of lenses, a four-layer retina and the ability to swivel their eyes and integrate images from different stages in the scan.
The downside is that the scanning and integrating processes are relatively slow. There are spiders with a reduced number of eyes, of these those with six-eyes are the most numerous and are missing a pair of eyes on the anterior median line others species have four-eyes and some just two.
Cave dwelling species have no eyes, or possess vestigial eyes incapable of sight. As with other arthropods, spiders’ cuticles would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact, spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called setaerespond to different levels of force, from strong contact to very weak air currents.
Chemical sensors provide equivalents of taste and smelloften by means of setae. Males have more chemosensitive hairs on their pedipalps than females. They have been shown to be responsive to sex pheromones produced by females, both contact and air-borne. In web-building spiders, all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively.
Like most arthropods, spiders lack balance and acceleration sensors and rely on their eyes to tell them which way is up. Arthropods’ proprioceptorssensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood.
On the other hand, little is known about what other internal sensors spiders or other arthropods may have. Each of the eight legs of a spider consists of seven distinct parts.
The part closest to and attaching the leg to the cephalothorax is the coxa ; the next segment is the short trochanter that works as a hinge for the following long segment, the femur ; next is the spider’s knee, the patellawhich acts as the hinge for the tibia ; the metatarsus is next, and it connects the tibia to the tarsus which may be thought of as a foot of sorts ; the tarsus ends in a claw made up of either two or three points, depending on the family to which the spider belongs.
Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors.
Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine hairs between the paired claws at the tips of their legs. These tufts, known as scopulaeconsist of bristles whose ends are split into as many as 1, branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings.
It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces. The abdomen has no appendages except those that have been modified to form one to four usually three pairs of short, movable spinneretswhich emit silk. Each spinneret has many spigotseach of which is connected to one silk gland. There are at least six types of silk gland, each producing a different type of silk.
Silk is mainly composed of a protein very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein.
In other words, it can stretch much further before breaking or losing shape. Some spiders have a cribelluma modified spinneret with up to 40, spigots, each of which produces a single very fine fiber.
The fibers are pulled out by the calamistruma comb-like set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However, most modern groups of spiders have lost the cribellum.
Tarantulas also have silk glands in their feet. Araneomorphar species that do not build webs to catch prey use silk in several ways: Spiders reproduce sexually and fertilization is internal but indirect, in other words the sperm is not inserted into the female’s body by the male’s genitals but by an intermediate stage. Unlike many land-living arthropods male spiders do not produce ready-made spermatophores packages of spermbut spin small sperm webs on to which they ejaculate and then transfer the sperm to special syringe -like structures, palpal bulbs or palpal organs, borne on the tips of the pedipalps of mature males.
When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or “safety ropes”, the male can identify the species and sex of these objects by “smell”. Spiders generally use elaborate courtship araneomoephae to prevent the large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating.
In web-weaving species, precise patterns of vibrations in the web are a major part spideds the rituals, while patterns of touches on the female’s body are important in many spiders that hunt actively, and may “hypnotize” the female.
Gestures and s;iders by the male are important for jumping spiderswhich have excellent eyesight. If courtship is successful, the male injects his sperm from the palpal bulbs into the female’s genital opening, known as the epigyneon the underside of her abdomen. Female’s reproductive tracts vary from simple tubes to systems that include seminal receptacles in which females store sperm and release it when they are ready. The only known exception is a spider from Israel, Harpactea sadisticawhich has evolved traumatic insemination.
In this species the male will penetrate its pedipalps through the female’s body wall and inject his sperm directly into her ovaries, where the embryos inside the fertilized eggs will start to develop before being laid. Males of the genus Tidarren amputate one of their palps before maturation and enter adult life with one palp only.