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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 .
The oldest known arachnid is the trigonotarbid Palaeotarbus jerami, from about in the Silurian period. [101] Note 3 ] Attercopus fimbriunguis , from 386 million years ago in the Devonian period, bears the earliest known silk-producing spigots, but its lack of spinnerets means it was not one of the true spiders , [ 103 ] which first appear in ...
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]
The saliva of the arthropod may contain anticoagulants, as in insects and arachnids which feed from blood. Feeding bites may also contain anaesthetic , to prevent the bite from being felt. Feeding bites may also contain digestive enzymes , as in spiders ; spider bites have primarily evolved to paralyse and then digest prey.
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.