Arachnid. Almost all extant arachnids are terrestrial. However, some inhabit freshwater environments and, with the exception of the pelagic zone, marine environments as well. They comprise over 100,000 named species, including spiders, scorpions, harvestmen, ticks, mites and Solifugae.[3] Anatomy[edit] Like all arthropods, arachnids have an exoskeleton, and they also have an internal structure of cartilage-like tissue called the endosternite, to which certain muscle groups are attached. The endosternite is even calcified in some Opiliones.[6] Locomotion[edit] Physiology[edit] Further adaptations to terrestrial life are appendages modified for more efficient locomotion on land, internal fertilisation, special sensory organs, and water conservation enhanced by efficient excretory structures as well as a waxy layer covering the cuticle.
The blood of arachnids is variable in composition, depending on the mode of respiration. Diet and digestive system[edit] Senses[edit] Reproduction[edit] Systematics[edit] Spider. Order of arachnids 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. Description Body plan Palystes castaneus female dorsal aspect 1: pedipalp 2: trichobothria 3: carapace of prosoma (cephalothorax) 4: opisthosoma (abdomen) 5: eyes – AL (anterior lateral) AM (anterior median) PL (posterior lateral) PM (posterior median) Leg segments: 6: costa 7: trochanter 8: patella 9: tibia 10: metatarsus 11: tarsus 13: claw 14: chelicera Nos 1 to 14 as for dorsal aspect I, II, III, IV = Leg numbers from anterior to posterior Circulation and respiration A syrphid fly captured in the web of a spider Central nervous system Eyes Size.
Scorpion. Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognised by the pair of grasping pedipalps and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger. Scorpions range in size from 9 mm (Typhlochactas mitchelli) to 20 cm (Hadogenes troglodytes).[1] Scorpions are found widely distributed over all continents, except Antarctica, in a variety of terrestrial habitats except the high latitude tundra. Scorpions number about 1750 described species,[2] with 13 extant families recognised to date. Scorpion venom has a fearsome reputation, but only about 25 out of over 1700 species are known to have venom capable of killing a human being.[3]:1 Etymology[edit] Geographical distribution[edit] Scorpions are found on all major land masses except Antarctica.
Classification[edit] Systematics[edit] Order Scorpiones Fossil record[edit] Morphology[edit] Mesosoma[edit] Opiliones. Opiliones (Latin opilio, "shepherd"; formerly Phalangida) are an order of arachnids commonly known as harvestmen. As of December 2011[update], over 6,500 species of harvestmen have been discovered worldwide,[1] although the real number of extant species may exceed 10,000.[2] The order Opiliones includes four suborders: Cyphophthalmi, Eupnoi, Dyspnoi, and Laniatores, and representatives of each can be found on every continent except Antarctica (with the exception of Dyspnoi, which is restricted to North America and Eurasia).
Well-preserved fossils have been found in the 400-million-year-old Rhynie cherts of Scotland, which look surprisingly modern, indicating that their basic body plan appeared very early on, and, at least in some taxa, has changed little since that time. Physical description[edit] The feeding apparatus (stomotheca) differs from most arachnids in that Opiliones can swallow chunks of solid food, not only liquids. The legs continue to twitch after they are detached. Tick. Taxonomy[edit] The Argasidae contain 193 species, although the composition of the genera is less certain, and more study is needed before the genera can become stable.[5] The currently accepted genera in 2010 are Antricola, Argas, Nothaspis, Ornithodoros, and Otobius.[5] Though common in North America, they feed rapidly, primarily on birds, and are very rarely found to parasitize land mammals or humans.[8] The family Nuttalliellidae contains only a single species, Nuttalliella namaqua, a tick found in southern Africa from Tanzania to Namibia and South Africa,.[5][9] It can be distinguished from ixodid ticks and argasid ticks by a combination of characteristics, including the position of the stigmata, lack of setae, strongly corrugated integument, and the form of the fenestrated plates.[10] Fossilized ticks are common.
Range and habitat[edit] Anatomy and physiology[edit] Diet and feeding behaviors[edit] A questing tick Legs[edit] Adult ticks have eight legs. Life cycle and reproduction[edit] Mite. Mites, along with ticks, are small arthropods belonging to the subclass Acari (also known as Acarina) and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology. In soil ecosystems, mites are favored by high organic matter content and by moist conditions, wherein they actively engage in the fragmentation and mixing of organic matter.[1] Diversity and systematics[edit] Some of the plant pests include the so-called spider mites (family Tetranychidae), thread-footed mites (family Tarsonemidae), and the gall mites (family Eriophyidae). Among the species that attack animals are members of the sarcoptic mange mites (family Sarcoptidae), which burrow under the skin. Insects may also have parasitic mites.
The tropical species Archegozetes longisetosus is one of the strongest animals in the world, relative to its mass (100 μg): It lifts up to 1,182 times its own weight, over five times more than would be expected of such a minute animal.[3] Notes.