The abdomen, referred to as the opisthosoma, is made up of twelve segments, each protected by sclerotized plates (called tergites above and sternites below).

[6] Pseudoscorpions spin silk from a gland in their jaws to make disk-shaped cocoons for mating, molting, or waiting out cold weather, but they do not have book lungs like true scorpions and the Tetrapulmonata.

Instead, they breathe exclusively through tracheae, which open laterally through two pairs of spiracles on the posterior margins of the sternites of abdominal segments 3 and 4.

Members of the Cheliferoidea (Atemnidae, Cheliferidae, Chernetidae and Withiidae) have an elaborate mating dance, which ends with the male navigating the female over his spermatophore.

They range worldwide, even in temperate to cold regions such as Northern Ontario and above the timberline in Wyoming's Rocky Mountains in the United States and the Jenolan Caves of Australia, but have their most dense and diverse populations in the tropics and subtropics, where they spread even to island territories such as the Canary Islands, where around 25 endemic species have been found.

The oldest known fossil pseudoscorpion, Dracochela deprehendor is known from cuticle fragments of nymphs found in the Panther Mountain Formation near Gilboa in New York, dating to the mid-Devonian, around 383 million years ago.

[23] It has all of the traits of a modern pseudoscorpion, indicating that the order evolved very early in the history of land animals.

[26] The only fossil from this time gap is Archaeofeaella from the Triassic of Ukraine, approximately 227 million years ago, which is suggested to be an early relative of the family Feaellidae.

Another reference in the 1780s, when George Adams wrote of "a lobster-insect, spied by some labouring men who were drinking their porter, and borne away by an ingenious gentleman, who brought it to my lodging.

[31] †Dracochelidae Pseudotyrannochthoniidae Chthoniidae Pseudogaryptidae Feaellidae Ideoroncidae Bochicidae Hyidae Syarinidae Parahyidae Gymnobisiidae Neobisiidae Geogarypidae Hesperolpiidae Garypidae Menthidae Olpiidae Garypinidae Larcidae Cheiridiidae Pseudochiridiidae Sternophoridae Withiidae Atemnidae Cheliferidae Chernetidae