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The Malpighian tubule system is a type of excretory and osmoregulatory system found in some insects, myriapods, arachnids and tardigrades. It has also been described in some crustacean species, [ 1 ] and is likely the same organ as the posterior caeca which has been described in crustaceans.
Arachnids are arthropods in the class Arachnida (/ ə ˈ r æ k n ɪ d ə /) of the subphylum Chelicerata. Arachnida includes, among others, spiders , scorpions , ticks , mites , pseudoscorpions , harvestmen , camel spiders , whip spiders and vinegaroons .
Basic characteristics of arachnids include four pairs of legs (1) and a body divided into two segments: the cephalothorax (2) and the abdomen (3). The ventral side of a brown widow spider. The epigastric plates and furrow are visible, as well as the hourglass marking on the underside of the abdomen, which is a characteristic feature of widow ...
Arachnid locomotion is the various means by which arachnids walk, run, or jump; they make use of more than muscle contraction, employing additional methods like hydraulic compression. [ 1 ] [ 2 ] Another adaptation seen especially in larger arachnid variants is inclusion of elastic connective tissues .
Ricinulei are unique among arachnids in that the first one to be discovered was a fossil, described in 1837 by the noted English geologist William Buckland; [26] albeit misinterpreted as a beetle. Further fossil species were added in subsequent years by, among others, Samuel Hubbard Scudder , Reginald Innes Pocock and Alexander Petrunkevitch .
The arachnid slit sensilla corresponds to the campaniform sensilla found in insects. [1] Slit sensilla tend to be widely distributed over the arachnid's exoskeleton, [3] but have also been found to be grouped at specific locations and in a bundle of parallel lines; the latter distribution is referred to as a "lyriform organ". [4]
Unlike arachnids with book lungs (scorpions, most spiders and several others), harvestmen and most other purely tracheate arachnids lack extensive arterial branching and well-defined venous sinuses. The circulatory system consists mainly of a dorsal tubular heart with anterior and posterior aortae. The heart is innervated by a cardiac ganglion.
Arachnology is the scientific study of arachnids, which comprise spiders and related invertebrates such as scorpions, pseudoscorpions, and harvestmen. Those who study spiders and other arachnids are arachnologists. More narrowly, the study of spiders alone (order Araneae) is known as araneology. [1]