Temporal range: Cenomanian–Recent
|Families & genera|
Palpigrades, commonly known as microwhip scorpions, are arachnids belonging to the order Palpigradi.
Palpigrades belong to the arachnid class. 3 millimetres (0.12 in) in length, and averaging 1–1.5 mm (0.04–0.06 in). They have a thin, pale, segmented integument, and a segmented abdomen that terminates in a whip-like flagellum. This is made up of 15 segment-like parts, or "articles", and may make up as much as half the animal's length. Each article of the flagellum bears bristles, giving the whole flagellum the appearance of a bottle brush. The carapace is divided into two plates between the third and fourth leg pair of legs. They have no eyes.They are the sister group to Thelyphonida, or whip scorpions, no more than
As in some other arachnids, the first pair of legs is modified to serve as sensory organs, and are held clear of the ground while walking. Unusually, however, palpigrades use their pedipalps for locomotion, so that the animal appears to be walking on five pairs of legs.
Some palpigrades have three pairs of abdominal lung-sacs, although these are not true book lungs as there is no trace of the characteristic leaflike lamellae which defines book lungs. However, many species have no respiratory organs at all and breathe directly through the cuticle.
Their exoskeleton is very weakly sclerotized compared to other arachnids, which is the reason why fossils are so rare, and go no further back than 99 million years ago in Burmese Amber.
Species of Palpigradi live interstitially in wet tropical and subtropical soils.A few species have been found in shallow coral sands and on tropical beaches. In Europe, they have been found in caves and underground spaces. There is one endemic species on the island of Malta, in the Mediterranean Sea, which exists only in one specific cave. They need a damp environment to survive, and they always hide from light, so they are commonly found in the moist earth under buried stones and rocks. They can be found on every continent, except in Arctic and Antarctic regions. Terrestrial Palpigradi have hydrophobic cuticles, but littoral (beach-dwelling) species are able to pass through the water surface easily.
Very little is known about palpigrade behavior.They are generally believed to be predators like their larger relatives, feeding on minuscule animals in their habitat. However, their chelicerae have been described as "more like a comb or brush than the forceps of a predator", and the species Eukoenenia spelaea has been shown to feed on cyanobacteria ("blue-green algae"). Their mating habits are unknown, except that they lay only a few relatively large eggs at a time.
By 2003, approximately 79 species of palpigrades had been described worldwide, in two families, containing a total of 7 genera.The two families are differentiated by the presence of ventral sacs on sternites IV–VI in Prokoeneniidae, and their absence in Eukoeneniidae.
Two fossil palpigrade species have been described. The first one is from the Onyx Marble of Arizona, which is probably of Pliocene age.Its familial position is uncertain. The second one ( Electrokoenenia yaksha), belonging to the family Eukoeneniidae, is known from Cretaceous (Cenomanian) amber from northern Myanmar. Older publications refer to a fossil palpigrade (or palpigrade-like animal) from the Jurassic of the Solnhofen limestone in Germany, but this has now been shown to be a misidentified fossil insect.
The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, arachnids, and several extinct lineages, such as the eurypterids.
Arachnida is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Spiders are the largest order in the class, which also includes scorpions, ticks, mites, harvestmen, and solifuges. In 2019, a molecular phylogenetic study also placed horseshoe crabs in Arachnida.
A pseudoscorpion, also known as a false scorpion or book scorpion, is an arachnid belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida.
Amblypygi is an ancient order of arachnid chelicerate arthropods also known as whip spiders and tailless whip scorpions. The name "amblypygid" means "blunt tail", a reference to a lack of the flagellum that is otherwise seen in whip scorpions. They are harmless to humans. Amblypygids possess no silk glands or venomous fangs. They rarely bite if threatened, but can grab fingers with their pedipalps, resulting in thorn-like puncture injuries.
Schizomida is an order of arachnids, generally less than 5 millimetres (0.20 in) in length.
The Opiliones are an order of arachnids colloquially known as harvestmen, harvesters, or daddy longlegs. As of April 2017, over 6,650 species of harvestmen have been discovered worldwide, although the total number of extant species may exceed 10,000. The order Opiliones includes five suborders: Cyphophthalmi, Eupnoi, Dyspnoi, Laniatores, and Tetrophthalmi, which were named in 2014.
The order Ricinulei is a group of arachnids known as hooded tickspiders, though they are not true spiders. Like most arachnids, they are predatory, eating small arthropods. In older works they are sometimes referred to as Podogona.
A book lung is a type of respiration organ used for atmospheric gas exchange that is found in many arachnids, such as scorpions and spiders. Each of these organs is found inside an open ventral abdominal, air-filled cavity (atrium) and connects with the surroundings through a small opening for the purpose of respiration.
Mites are small arthropods belonging to the class Arachnida and the subclass Acari. Mites are not a clade as they span two different groups of arachnids: the Acariformes are sister to the camel spiders, while the Parasitiformes are sister to the false scorpions; also, they exclude the ticks, order Ixodida, although ticks and mites are closely related. Mites are distantly related to spiders and scorpions.
The Mesothelae are a suborder of spiders that includes a single living (extant) family, Liphistiidae, and a number of extinct families. This suborder is thought to form the sister group to all other living spiders, and to retain ancestral characters, such as a segmented abdomen with spinnerets in the middle and two pairs of book lungs. Members of Liphistiidae are medium to large spiders with eight eyes grouped on a tubercle. They are found only in China, Japan, and southeast Asia.
Solifugae is an order of animals in the class Arachnida known variously as camel spiders, wind scorpions, sun spiders, or solifuges. The order includes more than 1,000 described species in about 153 genera. Despite the common names, they are neither true scorpions nor true spiders. Much like a spider, the body of a solifugid has two tagmata: an opisthosoma (abdomen) behind the prosoma. At the front end, the prosoma bears two chelicerae that, in most species, are conspicuously large. The chelicerae serve as jaws and in many species also are used for stridulation. Unlike scorpions, solifugids do not have a third tagma that forms a "tail". Most species of Solifugae live in dry climates and feed opportunistically on ground-dwelling arthropods and other small animals. The largest species grow to a length of 12–15 cm (5–6 in), including legs. A number of urban legends exaggerate the size and speed of the Solifugae, and their potential danger to humans, which is negligible.
Opilioacariformes is the smallest order of mites, containing a single family, and around 10 genera. They are rare, large mites, and are widely considered primitive, as they retain six pairs of eyes, and abdominal segmentation. Opilioacariformes may be the sister group to the Parasitiformes.
Tetrapulmonata is a non-ranked supra-ordinal clade of arachnids. It is composed of the extant orders Thelyphonida, Schizomida, Amblypygi and Araneae (spiders). It is the only supra-ordinal group of arachnids that is strongly supported in molecular phylogenetic studies. Two extinct orders are also placed in this clade, Haptopoda and Uraraneida. In 2016, a newly described fossil arachnid, Idmonarachne, was also included in the Tetrapulmonata; as of March 2016 it has not been assigned to an order.
The evolution of spiders has been going on for at least 380 million years, since the first true spiders evolved from crab-like chelicerate ancestors. More than 45,000 extant species have been described, organised taxonomically in 3,958 genera and 114 families. There may be more than 120,000 species. Fossil diversity rates make up a larger proportion than extant diversity would suggest with 1,593 arachnid species described out of 1,952 recognized chelicerates. Both extant and fossil species are described yearly by researchers in the field. Major developments in spider evolution include the development of spinnerets and silk secretion.
The Maltese palpigrade, endemic to the Maltese Islands, comes from the order Palpigradi, a rather primitive order of arachnids. There are 80 species of palpigrade worldwide. They are small and eyeless with a long tail-like structure.
An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda, which includes insects, arachnids, myriapods, and crustaceans. The term Arthropoda as originally proposed refers to a proposed grouping of Euarthropods and the phylum Onychophora.
Burmese amber, also known as Burmite or Kachin amber, is amber from the Hukawng Valley in northern Myanmar. The amber is dated to around 99 million years old, during the earliest part of the Cenomanian age of the Late Cretaceous. The amber is of significant palaeontological interest due to the diversity of flora and fauna contained as inclusions, particularly arthropods including insects and arachnids but also birds, lizards, snakes, frogs and fragmentary dinosaur remains. The amber has been known and commercially exploited since the first century AD, and has been known to science since the mid-nineteenth century. Research on the deposit has attracted controversy due to its role in funding internal conflict in Myanmar and hazardous working conditions in the mines where it is collected.
Electrokoenenia yaksha is a Palpigrade that lived approximately 100 million years ago during the Cretaceous period. It is the first microwhip scorpion fossil from this period to be found and is currently the oldest known Palpigrade.
Uraraneida is an extinct order of arachnids, known from fossils of Middle Devonian, Permian and possibly Cretaceous age. Two genera of fossils have been definitively placed in this order: Attercopus from the Devonian of United States and Permarachne from the Permian of Russia. In 2018, a third genus Chimerarachne, from the Cretaceous of Myanmar was proposed to belong to this group, but this placement is disputed. When the first fossils were found, they were identified as spiders, but now constitute the Uraraneida, a separate but closely related group.
Chimerarachne is a genus of extinct arachnids containing a single species Chimerarachne yingi. Fossils of Chimerarachne were discovered in Burmese amber from Myanmar which dates to the mid-Cretaceous, about 100 million years ago. Its classification is disputed, either belonging to Uraraneida a group otherwise known from the Devonian to Permian, or a separate clade closer to spiders. Since the earliest spider fossils are from the Carboniferous, either answer results in an at least a 170 myr ghost lineage with no fossil record, making it a Lazarus taxon. The size of the animal is quite small, being only 2.5 mm in body length, with the tail being about 3mm in length. These fossils resemble spiders in having two of their key defining features: spinnerets for spinning silk, and a modified male organ on the pedipalp for transferring sperm. At the same time they retain a whip-like tail, rather like that of a whip scorpion and uraraneids. Chimerarachne is not ancestral to spiders, being much younger than the oldest spiders which are known from the Carboniferous, but it appears to be a late survivor of an extinct group which was probably very close to the origins of spiders. It suggests that there used to be spider-like animals with tails which lived alongside true spiders for at least 200 million years.
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