Arachnids of the World, Unite! Quiz

Answer:

How to tell an arachnid from an insect: insects have six legs, a body that usually has three segments, and often antennae and/or wings; arachnids have eight legs, a body with two segments, and no antennae or wings. As well as the eight legs, they usually have another pair of appendages, the pedipalps, which may be used for feeding, but also for locomotion and/or reproduction. The two body parts are often called the cephalothorax and the abdomen, but these terms are misleading, as they suggest an internal anatomy which is not generally present, so the terms prosoma and opisthosoma are preferred.

There are over 100,000 extant species of arachnids (and more being discovered all the time), with such varied characteristics that the taxonomic categorisation within the class Arachnida is far from stable. There are multiple different category structures currently proposed, intending to establish nomenclature that accurately indicates the relationships between them all. However, classification based on externally visible traits and fossil records has been challenged by genetic analysis that suggests evolutionary divergence at different times and in different stages. For this reason, this quiz will not even attempt to provide detailed taxonomy about the examples chosen, most of which are names for groups that contain numerous genera and species.

The groups represented here are (in alphabetical order) Acariformes (dust mite, chigger), Amblypygi (whip-spider), Araneae (tarantula, huntsman), Opiiliones (harvestman), Palpigradi (microwhip scorpion), Parisitiformes (kiwi tick, Australian paralysis tick), Pseudoscorpionida (pseudoscorpion), Ricinulei (hooded tickspider), Schizomida (Australian spricket), Scorpiones (scorpion), Solifugae (camel spider) and Uropygi (vinegaroon).

Acariformes are mites. Dust mites are often found in house dust, and are responsible for allergies in some people. Chiggers are a type of mite whose parasitical larvae feed on animal skin cells, and can cause intense itching and irritation.

Amblypygi are often called whip-spiders or tailless whip-scorpions. Their front pair of legs are modified to be used as sensory organs, rather than for locomotion, and can be as much as five times as long as the body.

Araneae, the order which contains by for the most known species, will be the arachnids most familiar to players - spiders. The name arachnid comes from the Greek word for spider, 'arachne', itself derived from a myth about a woman named Arachne who considered herself a better weaver than the goddess Athena, and got turned into a spider for her efforts. The Latin 'araneus' is cognate to 'arachne', so used as the name for the order. Despite this source, not all spiders weave webs. The tarantula is an example of Mygalomorphae, a family of large hairy spiders who do not generally spin webs. A number of similar-looking spiders are often mistakenly called tarantulas, including the huntsman spider, also called a giant crab spider, which belongs to the Sparassidae family.

Opiliones are generally recognised because their legs are very long in proportion to their body, leading to a common name of daddy long-legs. The reason they are called harvestmen is obscure, but possibly related to the shape of their legs, which (vaguely, in my opinion) resemble the shape of a sickle used to harvest crops.

Palpigradi are quite small, both in number of species and in size. Many of them are only about a millimetre long, with a whiplike 'tail' (technically a flagellum) making up half of that length.

Parisitiformes, closely related to Acariformes, are the order which contains ticks of all shapes and sizes. Many ticks are vectors which can transmit disease to humans, and some (such as the Australian paralysis tick) actually inject a toxin when they bite which can be deadly if left untreated. The kiwi tick is endemic to New Zealand, where it is parasitic on their national bird, the kiwi.

Pseudoscorpionida are pretty clearly named - they resemble scorpions, but in a smaller scale (2-5 mm in length). The most widespread species is Chelifer cancroides, often called the house pseudoscorpion, which feasts on dust mites and booklice.

Ricinulei are another order which is small in both number and size, and few of them have common names. This may in part be because they are found in leaf litter inside caves in only a few parts of the world, so there is not a lot of human interaction. Some older books refer to them as hooded tickspiders, because of the hood that can be raised or lowered over their head. The fossil record shows various members of this order appearing and disappearing over time, which has led to them being dubbed a Lazarus taxon.

Schizomida is an order also called short-tiled whip-scorpions, of which the Australian spricket is an example. It should be noted that the Australian spricket was specified, as in other parts of the world the name spricket is given to an insect, also known as the spider cricket. No extant schizomids have eyes, but a few species have vestigial eyespots, which are sensitive to light/dark changes.

Scorpiones are the true scorpions, unlike several of the other orders whose name indicates similarity to the scorpions. Their distinguishing features include the development of their pedipalps into grasping pincers, and the narrow, segmented, stinger-tipped tail that curves forward over their back. Most species are found in desert areas, but some can be found almost anywhere. Their sting is used both as a defense and to kill prey. While a scorpion sting is painful to humans, fewer that one percent of scorpions species have a sting which is dangerous to humans.

Solifugae are also known regionally as sun spiders, camel spiders, and wind scorpions - despite the fact that they are not spiders or scorpions. The name solifuge comes from Latin words meaning sun-fleeing, reflecting their preference for dark spots; many live in underground burrows. Sun spider (or sunspider) seems to be a reference to their avoidance of the sun, not any kind of sunbathing behaviour. They have oddly humped heads - hence the camel appellation. The name wind scorpion refers to the swiftness of their movement.

Uropygi are also called Thelyphonida by some; and, confusingly, both terms can be more broadly used to include not only the whip scorpions, but also the schizomids (short-tailed whip scorpions). I told you that arachnid taxonomy is complicated! In the narrow sense, they are a group that resembles true scorpions in structure, but which also discharge a liquid containing acetic acid as a defense mechanism - hence several common names referring to vinegar.

As mentioned in the introduction, all of the incorrect options are insects.