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The authors favoured relationships shown by more slowly evolving genes, which demonstrated the monophyly of Chelicerata, Euchelicerata and Arachnida, as well as of some clades within the arachnids. The diagram below summarizes their conclusions, based largely on the 200 most slowly evolving genes; dashed lines represent uncertain placements.
The group's origins lie within an arachnid sub-group defined by the presence of book lungs (the tetrapulmonates); [1] [2] the arachnids as a whole evolved from aquatic chelicerate ancestors. More than 45,000 extant species have been described, organised taxonomically in 3,958 genera and 114 families. [3] There may be more than 120,000 species. [3]
The cephalothorax, also called prosoma, is composed of two primary surfaces: a dorsal carapace and a ventral sternum.Most external appendages on the spider are attached to the cephalothorax, including the eyes, chelicerae and other mouthparts, pedipalps and legs.
Close-up of the chelicerae of a harvestman. The chelicerae consist of three segments, with the distal two forming a pincer [3] equipped with a row of teeth. Based on developmental gene expression data, the proximal segment is thought to be homologous to the femur and patella of the legs, the middle segment to the tibia through the tarsus of the legs, and the distal segment to the apotele (the ...
Diagram of a prawn, with the carapace highlighted in red. A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.
Opiliones' own divergence is dated to 414 million years ago, which arachnid are estimated to have originated during the late Cambrian to early Ordivician. [ 10 ] Genetic analysis performed on a modern Phalangium opilio specimen found that a suppressed gene that, if active, would generate a second pair of eyes at the lateral location, providing ...
Printable version; In other projects Wikimedia Commons; Wikidata item; ... Pages in category "Arachnid genera" The following 30 pages are in this category, out of 30 ...