Comprehensive Description

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Comprehensive Description

The Amblypygi are a group of around 150 species of arachnids commonly known as tailless whip scorpions or whip spiders (Harvey 2002, 2003). In contrast to the Uropygi [=Thelyphonida] (whip scorpions or vinegaroons), amblypygids lack a tail. The long, bulky, and spined pedipalps extending in front of their somewhat flattened bodies are raptorial (i.e., adapted for seizing prey) and the first pair of walking legs are highly modified into very long antenna-like sensory appendages. Amblypygids lack the silk-spinning spinnerets or poison glands of spiders, but their chelicerae are modified as spider-like fangs. (Barnes 1987; Brusca and Brusca 2003) Either the Uropygi or Araneae (spiders) are believed to be the sister clade to the Amblypygi, with Uropygi generally viewed as more likely given current knowledge (Weygoldt 2000; Fahrein et al. 2009).

Amblypygids are widely distributed in warm, humid regions, where they are typically found in protected situations such as under bark or in leaf litter. Some live in caves. Most species are less than 5 cm long (the smallest is less than a centimeter), but the antenniform first pair of legs may be as long as 25 cm. These long "legs" function as both touch receptors and chemoreceptors. Amblypygids hunt at night, walking sideways with their front "legs" extended. When a prey item is encountered, it is grabbed with the pedipalps and torn open with the chelicerae, allowing the body fluids to be imbibed. (Barnes 1987; Brusca and Brusca 2003)

In the few amblypygid species in which reproductive behavior has been observed, the male courts the female with trembling movements of the antenniform legs and rocking body movements directed toward the female. Eventually, a sperm-containing spermatophore is deposited. Using his pedipalps or front legs, the male guides the female over the spermatophore, which she takes up. After fertilization occurs, the female produces a parchment-like membrane that holds her 6 to 60 large eggs underneath her abdomen. She carries the eggs until hatching and subsequently carries the newly hatched offspring. After their first molt, the young amblypygids climb onto the mother's abdomen until the next molt. (Barnes 1987; Brusca and Brusca 2003)

Amblypygids typically feed on arthropods such as crickets, katydids, harvestmen, spiders, millipedes, roaches, and moths (which they are able to snatch out of the air!) (Hebets 2002), but Ladle and Velander (2003) reported a very unusual feeding habit for a Caribbean species inhabiting rocky outcrops adjacent to mountain streams running through primary tropical rainforest on the island of Tobago: here, Heterophrynus cheiracanthus were observed capturing and eating Macrobrachium prawns plucked from the stream.

Rayor and Taylor (2006) reported on their observations of social behavior in amblypygids, which are generally viewed as solitary animals, and review the literature on early parental care and more complex social behaviors in non-spider arachnids in general.

Weygoldt et al. (2010) described the mating and reproductive behavior of Phrynus exsul, the only Old World species of the family Phrynidae (an essentially Neotropical group), and compare it to that of other phrynids. The Neotropical Phrynus were revised by Quintero (1981).

Harvey (2003) provides a dichotomous key to families and a world catalogue of species. Weygoldt (2000) reviewed the biology of the Amblypygi and includes a key to genera as well as basic information about each genus (distinguishing characteristics, geographic distribution, key literature, etc.).


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© Shapiro, Leo

Source: EOL Rapid Response Team


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