Like all species in the family Hypochilidae, " Hypochilus thorelli " has four book lungs, like araneomorph spiders.
12.
The oldest book lungs have been recovered from extinct trigonotarbid arachnids preserved in the 410-million-year-old Rhynie chert of Scotland.
13.
Mantispids that board spiders usually adopt positions on or near the base of the abdomen; some species may enter the spider's book lungs.
14.
The second segment bears a pair of featherlike sensory organs known as the pectines; the final four segments each contain a pair of book lungs.
15.
Among smaller araneomorph spiders there are species in which the anterior pair of book lungs have also evolved into tracheae, or are simply reduced or missing.
16.
Each of the somites 3 to 7 bears a pair of spiracles; they serve as openings for the scorpion's respiratory organs, known as book lungs.
17.
Some palpigrades have three pairs of abdominal lung-sacs, although these are not true book lungs as there is no trace of the characteristic leaflike lamellae which defines book lungs.
18.
Some palpigrades have three pairs of abdominal lung-sacs, although these are not true book lungs as there is no trace of the characteristic leaflike lamellae which defines book lungs.
19.
Some flies in the family Acroceridae which are endoparasites of mygalomorphs may remain dormant in the book lungs for as long as 20 years before beginning their development and consuming the spider.
20.
Fossils of aquatic scorpions with gills appear in the Silurian and Devonian periods, and the earliest fossil of an air-breathing scorpion with book lungs dates from the Early Carboniferous period.
