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Order Palpigradi: Phylogeny & Examples

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

A cousin to spiders, ticks, and mites, members of Palpigradi are also known as the microscorpions. In this lesson, we'll take a closer look at this unique and tiny animal, which unlike its larger cousin the scorpion, poses no threat to you.

The Microscorpions

When you hear the word ''scorpion,'' does it make you cringe a little? Do you think of an insect with large front claws and a stinging tail? Does it make you anticipate a possible trip to the emergency room when that stinging tail injects you with venom?

Well, you can rest easy for now, because microscorpions, also called microwhip scorpions, are harmless creatures that belong to the order Palpigradi. They get their name from the fact that they do resemble scorpions and have a long tail-like structure, but aside from also belonging to the Arachnida class, this is where the similarities end.

Palpigrades, or microscorpions, are tiny animals that in some ways look like their cousin, the scorpion
a palpigrade

Class Arachnida, which includes animals like scorpions, spiders, ticks, and mites, belongs to the phylum Arthropoda, which is the largest and most diverse phylum of the animal kingdom. Arthropoda also includes familiar friends, such as insects and crustaceans, and considering that there are a possible 30 million species of insects on Earth, you can start to understand why this phylum is so large and varied.

Palpigradi itself has an estimated 80 different species that belong to two different families and six different genera. They are typically found in tropical and sub-tropical wet soils, under rocks, in caves, and other dark and humid places. In the United States they can be found in Texas and California, though you'll be hard pressed to see them, since they are only about 0.7-3 mm total in length! The feeling is mutual though, since palpigrades are eyeless animals. Since they are so cryptic and elusive, not much is known about palpigrade behavior. It's thought that they might be predators, but also that some may feed on blue-green algae.

Identifying Palpigradi

The two different families of Palpigradi can be differentiated by one distinct feature: a sac on the ventral, or underside, of the animal. Species in the family Prokoeneniidae have them and those in the family Eukoeneniidae do not.

You may have heard of whip scorpions, which belong to the order Thelyphonida (also called Uropygi). Considered cousins of the microscorpions, these animals are much larger and look quite a bit more like their other cousin, the true scorpions.

A cousin of Palpigradi is Thelyphonida, or the whip scorpion
whip scorpion

Like other members of Arachnida, palpigrades have modified front appendages that serve as sensory organs. But unlike other arachnids, palpigrades use these appendages for walking, which makes them appear to have five pairs of legs instead of the four we typically see in spiders and other similar animals.

If you're still not convinced you're dealing with a microscorpion, then take a look at the tail. In Palpigradi, this is comprised of 15 segments that can be as much as half of the animal's total length. This tail, which is actually a brittle flagellum, or tail-like structure that helps with locomotion, is covered in bristles and looks like a bottle-cleaning brush. And again, there's no venom in this tail so it can't harm you. And considering how small palpigrades are, even if it did sting, you probably wouldn't even notice!

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