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Secondary homology is implied by parsimony analysis, where a character state that arises only once on a tree is taken to be homologous. [20] [21] As implied in this definition, many cladists consider secondary homology to be synonymous with synapomorphy, a shared derived character or trait state that distinguishes a clade from other organisms.
The fibers are pulled out by the calamistrum, a comblike 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 ...
All of these terms are by definition relative, in that a trait can be a plesiomorphy in one context and an apomorphy in another, e.g. having a backbone is plesiomorphic between birds and mammals, but is apomorphic between them and insects.
More narrowly, the study of spiders alone (order Araneae) is known as araneology. [1] The word "arachnology" derives from the Greek words ἀράχνη, arachnē, "spider"; and -λογία, -logia, "the study of a particular subject". The greek word for "spider" itself refers to Arachne, the female protagonist of an ancient tale of the Greek ...
The extant chelicerates comprise two marine groups: Sea spiders and horseshoe crabs, and the terrestrial arachnids. These have been thought to be related as shown below. [41] [44] (Pycnogonida (sea spiders) may be excluded from the chelicerates, which are then identified as the group labelled "Euchelicerata". [46]) A 2019 analysis nests ...
Spider behavior refers to the range of behaviors and activities performed by spiders. Spiders are air-breathing arthropods that have eight legs and chelicerae with fangs that inject venom . They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms [ 1 ] which is reflected in their ...
Silk: spiders, silk moths, larval caddis flies, and the weaver ant all produce silken threads. [145] The praying mantis body type – raptorial forelimb, prehensile neck, and extraordinary snatching speed - has evolved not only in mantises but also independently in neuropteran insects Mantispidae. [146]
The arthropod head problem has been tackled in three main ways in this regard, first by using genetic segmental markers to probe the obscure region in front of the mouth, especially in insects; second by looking at Hox gene expression patterns to detect patterns of homology among different arthropods; and third, by studying gene expression in ...