Amblypygi
Order of arachnids
From Wikipedia, the free encyclopedia
Amblypygi is an order of arachnids also known as whip-spiders or tailless whip-scorpions. The name "amblypygid" means "blunt tail", a reference to a lack of the flagellum that is otherwise seen in whip-scorpions. Amblypygids possess no silk glands or venom. They rarely bite if threatened but can grab fingers with their pedipalps, resulting in thorn-like puncture-injuries.
| Amblypygi | |
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| Heterophrynus, Ecuador | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Class: | Arachnida |
| Clade: | Tetrapulmonata |
| Order: | Amblypygi Thorell, 1883 |
| Families | |
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| Synonyms[2] | |
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As of 2026[update], five families, 18 genera, and around 280 species had been discovered and described.[3] They are found in tropical and subtropical regions worldwide, mainly in warm and humid environments. They like to stay protected and hidden within leaf litter, caves, or underneath bark. Some species are subterranean; all are nocturnal. Fossilized amblypygids have been found dating back to the Carboniferous period, such as Weygoldtina.[1]
Description
Morphology
Being arachnids, Amblypygi possess two body segments; the prosoma and the opisthosoma (often referred to as the cephalothorax and abdomen), four pairs of legs, pedipalps, and chelicerae. The first pair of legs act as sensory organs and are not used for walking. The sensory legs are very thin and elongated, have numerous sensory receptors, and can extend several times the length of the body.[5] Their bodies are broad and highly flattened, with an undivided prosoma and a segmented opisthosoma.[6]Most species have eight eyes; a pair of median eyes at the front of the carapace above the chelicerae and 2 smaller clusters of three eyes each further back on each side.
Size
Amblypygids range from 5 to 29 cm (2.0 to 11.4 in) in walking legspan.[5][7][6] The elongated first pair of legs, however, can reach extreme lengths of up to 61 cm (24 in) in total. If sensory legs are counted, the largest amblypygid species are the largest arachnids in the world by legspan.[6] Some of the larger species of the genus Heterophrynus may be the largest of the amblypygi in walking and sensory legspan (or whipspan).[6] Previously autotomized whip legs that have regrown fully upon being regenerated grow even longer than their non-autotomized counterparts.[7]
The largest whipspider by body size is Acanthophrynus, another species with very large overall dimensions, with a total body length of up to 45 mm (1.8 in). Some species, especially those in the family Phrynichidae, also have extremely elongated pedipalps, with Euphrynichus reaching nearly 40 cm (16 in) across the extended pedipalps.[7]
Pedipalps
Amblypygids have raptorial pedipalps modified for grabbing and retaining prey, much like the forelegs of mantises.[8] The pedipalps are generally covered in spines, used for impaling and capturing prey. They are kept folded in front of the prosoma when not in use.[6] Whipspider pedipalps often display sexual dimorphism in their size and shape,[9] with males generally having longer pedipalps in sexually dimorphic species.[7]
Most whipspider species hold their pedipalps horizontally, folded in front of the body, when at rest, with only the joint between the pedipalp trochanter and femur allowing rotation into the vertical plane. Some species, such as those of the genus Phrynus, hold their pedipalp femurs vertically while hunting prey or during courtship.[7] The two species in the family Paracharontidae, the most basal extant amblypygid lineage and the only living paleoamblypygi, have pedipalps that articulate vertically,[10] as do ancient extinct species.[11] Many Charontid species fold the pedipalps at a more oblique angle in front of the body, closer to this ancestral configuration.[7]
Pedipalp morphology is often described, and taxa differentiated, with reference to the arrangement of the spines, particularly those of the tibia. Spines are divided into primary and secondary spines, the primary spines being those that are present in the earliest free living instars, with the secondary spines being added during later growth. Usually there are three primary spines present on the dorsal side of the pedipalp tibia, although Phrynus and Paraphrynus have 5 and 6 primary dorsal spines, respectively.[7]
Pedipalp morphology varies across the amblypygi, with configurations often conforming to a particular style of prey capture. The pedipalps of some genera, such as Euphrynicus and others in the family Phrynichidae, are extremely long, and free of large spines until near the extreme distal end of the appendage[6], where a jointed "hand" is formed from spines and the tarsus of the appendage[7]. Others have shorter pedipalps with an increased number of large dorsal and ventral spines, forming a "catching basket" for prey capture.
Legs
The walking legs of amblypygi are segmented into, in order proximally to distally, the coxa,[6] trochanter, femur, patella, tibia, and tarsus. The patella is typically short, and the joint between it and the tibia very inflexible. The tibia is divided into two segments, in proximal to distal order the basitibia and distitibia. In most species, the basitibia of the fourth leg is further divided into two to four articles, being undivided only in Phrynichus and Phrynichodamon. These inter-tibial joints are not muscled and can only be bent passively, for example during grooming with the pedipalps.[7]
Whipspiders autotomize their legs at the joint between the patella and tibia. The portion of the leg that is autotomized is then able to be regenerated, eventually reaching full size after multiple molts. Regeneration may alter the subdivision of the basitibia of walking legs.[7]
Amblypygi grasp the substrate on which they climb with the aid of tarsal claws at the tips of each walking leg,[7] similar to those present in spiders.[12] Additionally, some species, such as Paracharon and the Charontidae,[7] possess pulvilli (adhesive pads) on the tarses, allowing them to climb smooth surfaces such as glass.[6]
Exoskeleton
Whip-spiders are covered with a layer of a solidified secretion that forms a super-hydrophobic coating.[13] Studies on the spotted tailless whip-scorpion also show their exoskeleton is enriched with several trace-elements, including calcium, magnesium, manganese, potassium, sodium, and zinc, which tends to accumulate as the individual gets older. The same trace-elements are also present in the exoskeleton of the other members of Tetrapulmonata.[14] Like other arachnids, an amblypygid will molt several times during its life.[5] Molting is done while hanging from the underside of a horizontal surface in order to use gravity to assist in separating the old exoskeleton from the animal.
Anatomy
Circulatory system
Similarly to other arachnids, the circulatory fluid of amblypygi is known as hemolymph. It is analogous to the blood of vertebrates, but oxygen is attached to the copper-containing protein hemocyanin rather than hemoglobin. Hemocyanins are blue when oxygenated and colorless when deoxygenated, giving hemolymph a blueish color.[15]
As is the case with other arthropods, amblypygids have an open circulatory system. The heart consists of a muscular tube running lengthwise along the dorsal center of the opisthosoma. At its anterior end, its largest single connection, the aorta anterior transports blood to a large sinus and several branching aortas that supply blood to the chelicerae, pedipalps, legs, and organs of the prosoma. In the opisthosoma, lateral arteries branch directly off from the walls of the heart, supplying blood to the opisthosoma. A small aorta at the far posterior tip of the heart, the aorta posterior, also serves this purpose. Hemolymph flow is checked by passive valves at each aorta and artery connection to the heart, which open during the systole (heart contraction) and close during diastole, maintaining unidirectional flow of hemolymph.[16]
Respiration takes place in the book lungs on the underside of the opisthosoma. After supplying oxygen to the organs and tissues of the opisthosoma, hemolymph flows into a paired longitudinal ventral sinus.[16] It then flows through the sinuses surrounding the posterior and then anterior book lungs, becoming oxygenated. The oxygenated blood flows through two pulmo-pericardial sinuses to the pericardial sinus, surrounding the heart. From there, blood is drawn back into the heart through ostia—slit like openings in the side of the heart that open and close opposite to the aortic and arterial valves.[17]
Nervous system
The central nervous system of whipspiders is contained within the prosoma. Similarly to spiders, it is mainly composed of a supraesophageal ganglion and subesophageal ganglion, so named for their positions above and below the esophagus and sucking stomach, also located in the prosoma. The supraesophageal ganglion is also referred to as the "brain" of the amblypygid, and is smaller than the subesophageal. It contains the protocerebrum and connections to the eyes and chelicerae. The much larger subesophageal ganglion contains the ganglia of all the other limbs of the whipspider, and those of the opisthosoma.[18] Large mushroom bodies, the largest among all arthropods except horseshoe crabs, make up a large portion of the brain, receiving visual and olfactory sensory inputs.[19]
Distribution and Ecology
Distribution
Whipspiders are distributed worldwide within tropical and subtropical regions, with a small number of species occurring in more temperate areas. Genera are typically geographically restricted to specific areas of the world, although the genus Charinus is distributed worldwide. The family Phrynidae is distributed within the Neotropical realm, along with Charinus and one phrynichid genus, Trichodamon.[7]
The Phrynichidae occur within the tropical and subtropical regions of the old world. Most Phrynichid genera are distributed only within Africa, although Phrynichus also ranges into the Middle East, the Indian subcontinent, and Southeast Asia.[7] Enigmatically, one Asian Phrynid species, Phrynus exsul, has been described from Indonesia.[20]
The family Charontidae (including the now junior synonym Charinidae[11]) are most diversely distributed within Asia, although as mentioned previously Charinus is distributed worldwide. Charon ranges into Australia, representing the only Oceanian amblypygi.[7] Sarax ionniticus is the only whipspider found in Europe, distributed around the Eastern Mediterranean.[21]
Ecology
Amblypygi almost always prefer humid environments, although some species occur in arid regions. Caves and forests are very common habitats, with some species being entirely cave dwelling. Species that inhabit dry areas often seek out humid microhabitats, such as rock crevices, in order to conserve moisture, or have adaptations to make them more resistant to desiccation than other species.[7]
Behavior
Amblypygids have eight legs, but use only six for walking, often in a crab-like, sideways fashion. The front pair of legs are modified for use as antennae-like feelers, with many fine segments giving the appearance of a "whip". When suitable prey is located with the antenniform legs, the amblypygid seizes its victim with large spines on the grasping pedipalps, impaling and immobilizing the prey. This is typically done while climbing the side of a vertical surface and facing downward toward their prey.[22]
Reproduction
Courtship involves the male depositing a stalked spermatophore, which has one or more sperm masses at the tip, onto the ground, and using his pedipalps to guide the female over them.[23] She gathers the sperm and lays fertilized eggs into a sac carried under the abdomen, or opisthosoma. When the young hatch, they climb up onto the mother's back; any which fall off before their first molt will not survive.
Socialization
In common with most other arachnids,[24] adult whipspiders are not particularly social.[7] However, some species may be among the few examples of arachnids that exhibit social behavior. Research conducted at Cornell University with Phrynus marginemaculatus and Damon diadema suggests that mother amblypygids communicate with their young with their antenniform front-legs, and the offspring reciprocate both with their mother and siblings. The ultimate function of this social behavior remains unknown.[24] The amount of aggression between individuals can vary considerably even within a given genus, with Peter Weygoldt observing that Heterophrynus alces is extremely aggressive to conspecifics, while H. longicornis is often found in male-female pairs and tolerate the presence of other individuals far more. Amblypygids hold territories that they defend from other individuals.[25]
Diet
Whipspiders mostly prey upon invertebrates, particularly insects, but they are opportunistic and have also been observed feeding on vertebrates.[5][7] Amblypygids are generally sit-and-wait predators, especially larger species such as Heterophrynus. Young individuals and small species tend to forage more actively[7]. They generally do not feed for a period of time before, during, and after molting. Female whipspiders will also often refrain from eating while carrying an egg sac and during the early development of the young, often a period of over 3 months.[7]
Pincer-like chelicerae work to grind and chew the prey prior to ingestion. The tailless whip scorpion may go for over a month in which no food is eaten. Often this is due to pre-molt. Due to the lack of venom the tailless whip scorpion is very nervous in temperament, retreating away if any dangerous threat is sensed by the animal.[citation needed]
Taxonomic history
Whipspiders—at the time as a single species—were described in Carl Linnaeus's Systema Naturae, under the name Phalangium reniforme,[26] in a short section alongside Phalangium opilio, which has remained intact as its original usage as a harvestman. Linneus lists the habitat of P. reniforme as "in America." In the original Latin, he described its characteristics as:[27]
...antennis corpore longioribus, thorace reniformi.
Tarantula fusca major, pedibus anterioribus crassioribus aculeatis & unguiculatis fere cheliformibus, proximis longissimis & tenuissimis.
...with antennae longer than the body, and a kidney-shaped thorax.A large, dark tarantula; its front legs are thicker, spiny, and clawed—almost pincer-like—while the next pair are extremely long and slender.
— Carl Linnaeus, Systema Naturae, page 619
Peter Weygoldt included a tentative cladogram of the extant amblypygi in his 2000 book Whip Spiders (Chelicerata: Amblypygi): Their Biology, Morphology, and Systematics. The cladogram only showed "possible" relationships between the amblypygid genera, citing a need for a revision of the Charinidae and the uncertain placement of the genus Catageus. Weygoldt's 2000 cladogram approximation is as follows:[7]
| Amblypygi |
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Recent molecular analysis has refined whipspider phylogeny further. A 2024 paper incorporated genetic data from a newly discovered species within the Paracharontidae (since described as Jorottui[28]). Genomic data was not available prior to this new relict, as the only other living Paleoamblypygid, Paracharon caecus, was last collected in 1899. The new Paleoamblypygid allowed the first molecular phylogeny of the amblypygi, outlined below:[29]
| Amblypygi |
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The Authors of the 2024 study concluded that the family Charinidae was a junior synonym of Charontidae. The paper also uncovered several non-monophyletic groupings present within some current genera. For instance, Damon was indicated to be polyphyletic, entangled with Musicodamon and Phrynichodamon, and Phrynus and Heterophrynus were also recovered as polyphyletic.[29]
As pets
Several genera of Amblypygi are sold and kept as pets, including Acanthophrynus, Charinus, Charon, Damon, Euphrynichus, Heterophrynus, Phrynus, Paraphrynus, and Phrynichus.[30][6] Tailless whip-scorpions live anywhere between 5 and 10 years.[31][32]
Genera
The following genera are recognised:[33][34]
- Palaeoamblypygi Weygoldt, 1996
- Paracharontidae Weygoldt, 1996
- Paracharon Hansen, 1921 (1 species, West Africa)
- Jorottui Moreno-González, Gutierrez-Estrada, & Prendini, 2023 (1 species, northern South America)
- Weygoldtinidae Dunlop, 2018[35]
- †Weygoldtina Dunlop, 2018 (2 species, Upper Carboniferous Europe, North America)[35]
- Paracharontidae Weygoldt, 1996
- Euamblypygi Weygoldt, 1996
- †Paracharonopsis Engel & Grimaldi, 2014 (1 species, Cambay amber, India, Eocene)[36]
- Charinidae Weygoldt, 1996
- Charinus Simon, 1892 (33 species)
- Sarax Simon, 1892 (10 species)
- Weygoldtia Miranda, Giupponi, Prendini & Scharff, 2018 (3 species)
- Neoamblypygi Weygoldt, 1996
- Charontidae Simon, 1892
- Unidistitarsata Engel & Grimaldi, 2014
- †Kronocharon Engel & Grimaldi, 2014 (1 species, Burmese amber, Myanmar, Cretaceous)
- †Burmacharon? Hu et al. 2020 (1 species, Burmese amber, Myanmar, Cretaceous)
- Phrynoidea Blanchard, 1852
- Phrynichidae Simon, 1900
- Damon C. L. Koch, 1850 (10 species)
- Euphrynichus Weygoldt, 1995 (2 species)
- Musicodamon Fage, 1939 (1 species)
- Phrynichodamon Weygoldt, 1996 (1 species)
- Phrynichus Karsch, 1879 (16 species)
- Trichodamon Mello-Leitão, 1935 (2 species)
- Xerophrynus Weygoldt, 1996 (1 species)
- Phrynidae Blanchard, 1852
- Acanthophrynus Kraepelin, 1899 (1 species)
- †Britopygus Dunlop & Martill, 2002 (1 species; Crato Formation, Brazil, Cretaceous)
- Heterophrynus Pocock, 1894 (14 species)
- Paraphrynus Moreno, 1940 (18 species)
- Phrynus Lamarck, 1801 (28 species, Oligocene - Recent)
- Phrynichidae Simon, 1900
- Incertae sedis:
- † Sorellophrynus Harvey, 2002 (1 species, Upper Carboniferous, North America)
- † Thelyphrynus Petrunkevich, 1913 (1 species, Upper Carboniferous, North America)
