Pagkakaiba sa pagitan ng mga pagbago ng "Arachnida"

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<!-- '''Arachnids''' are a class ('''Arachnida''') of [[Arthropod|joint-legged]] [[invertebrate]] [[animal]]s in the subphylum [[Chelicerata]]. All arachnids have eight legs, but some exceptions are of some species having the first pair legs convert to sensory function and [[harvest mite]] larvae have only 3 pairs of legs. The term arachnid is from the [[Greek language|Greek]] word άράχνη or ''arachne'', meaning spider,<ref>{{cite encyclopedia|encyclopedia=[[Oxford English Dictionary]]|year=1989|edition=2nd edition|title=arachnid}}</ref> and also referring to the [[Greek mythology|mythological]] figure [[Arachne]].
 
Arachnids are chiefly terrestrial [[arthropod]]s, but are also found in freshwater and, with the exception of the [[pelagic zone]], in all marine environments. They comprise over 100,000 named [[species]], including [[spider]]s, [[scorpion]]s, [[opiliones|harvestmen]], [[tick]]s, and [[mite]]s.<ref>{{cite book|editor=Cracraft, Joel & Donoghue, Michael|title=Assembling the Tree of Life|publisher=Oxford University Press, USA|date=2004|page=297}}</ref>
 
It is commonly understood that arachnids have four pairs of legs, and that arachnids may be easily distinguished from [[insect]]s by this fact (insects have six legs or three pairs). Arachnids generally have a total of 6 pairs of appendages — two pairs of which have become adapted for feeding, defense, and sensory perception. The first pair of appendages, the [[chelicerae]], serve in feeding and defense. The next pair of appendages, the [[pedipalps]] have been adapted for feeding, locomotion, and/or [[reproduction|reproductive]] functions. In [[Solifugae]], the palpi are quite leg-like and make Solifugae appear to have ten legs. The [[larva]]e of mites (and [[Ricinulei]]) have only six legs; the fourth pair appears when they [[ecdysis|moult]] into [[nymph (biology)|nymph]]s. However, there are also adult mites with six, or even four legs.<ref name=schmidt93>Schmidt 1993: 58</ref>
 
Arachnids are further distinguished by the fact they have no [[antenna (biology)|antennae]] and no [[insect wing|wings]]. Their body is organized into two [[tagma]] called the [[prosoma]], or [[cephalothorax]], and the [[opisthosoma]], or [[abdomen]]. The [[cephalothorax]] (prosoma) is derived from the fusion of the [[cephalon]] (head) and the [[thorax]]. The [[abdomen]] (opisthosoma) can be further divided into the preabdomen and postabdomen in many taxa, although in some orders such as the [[Acari]] the abdominal sections are fused.<ref>Ruppert, E., Fox, R., & Barnes, R. (2007) Invertebrate Zoology: A functional evolutionary approach. 7th Edition. ''Thomson Learning'' ISBN 0-03-025982-7</ref>
 
There are some important modifications that are particularly important for the terrestrial lifestyle of an arachnid, such as internal respiratory surfaces in the form of [[Invertebrate trachea|trachea]], or modification of the [[book gill]] into a [[book lung]], an internal series of [[vascular]] [[lamellae]] used for [[gas exchange]] with the air. Further adaptations are [[appendages]] modified for more efficient [[locomotion]] on land, internal fertilisation, special sensory organs, and [[water]] conservation enhanced by more efficient [[excretory]] structures ([[coxal gland]]s and [[Malpighian tubules]]) as well as a waxy layer covering the cuticle.
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Ang mga araknid ay kalimitang [[carnivore|kumakain ng karne]]. Kumakain sila ng mga nauna nang natunaw na mga katawan ng mga kulisap at mga maliliit na hayop. Tanging ang mga [[harvestmen]] at mga [[mite]], gaya ng [[house dust mite]], na may makikitang pagkain ng solidong partikulo at ang pagbilad sa mga panloob na parasitiko <ref name=pinto2007>Pinto-da-Rocha, R., Machado, G. & Giribet, G. (2007) Harvestmen — The Biology of Opiliones. ''Harvard University Press'' ISBN 0-674-02343-9</ref>, subalit hindi katakatataka sa mga gagamba na kainin ang sarili nilang sapot. Maraming grupo ay [[kamandag (lason)|makamandag]]. Naglalabas sila ng mga kamandag gamit ang mga espesyal na mga [[glandula]] upang pumatay ng prey o kaya kalaban. Maraming mite ang mga [[parasitiko]] at kalimitang nagdadala ng [[sakit]]. Ang mga araknid ay kalimitang [[itlog (biyolohiya)|nangingitlog]] subalit may mga alakdan na nangaganak ng buhay na supling.
 
Totoong ang lahat ng mga arthropod ay may mga exoskeleton at may panloob na estraktura ng parang [[cartilage]] na tissue na tinatawag na [[endosternite]]. Maraming grupo ng masel ang nakadikit dito. Ang kalsipikasyon ng endosternite ay makikita sa ilang mga Opiliones. <ref>[http://www.ncbi.nlm.nih.gov/pubmed/750069]</ref>
 
Mayroong dalawang uri ng mga mata ang mga Araknid, ang lateral at median na [[ocelli]]. Ang lateral na ocelli nag-evolve mula sa mga [[matang kompawnd]] at mayroong [[tapetum lucidum|tapetum]] na tumtulong sa paghuli ng mga [[photon]]. Ang median na ocelli ay nagmula sa isang tuping transverse fold ng [[ectoderm]]. Ang mga ninuno ng mga makabagong araknid ay maaring may parehong uri ng mata ngunit ang mga makabago ay mayroong isa lamang sa dalawang uri.<ref name=pinto2007/>
 
==Sanggunian==
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