The bottom side of the abdomen is usually brown with yellow book lungs.

They do not have book lungs, and breathe through tracheae.

The book lungs of some early spiders can be seen in cross-sections.

Book lungs, something that works for a heart, musculature, exoskeleton.

These first scorpions had gills instead of the present forms' book lungs.

Like mygalomorph spiders, they have two pairs of book lungs.

Some arachnids have structures called "book lungs" used for atmospheric gas exchange.

Some species have three pairs of book lungs, while others have no respiratory organs at all.

They can stay underwater for over an hour, using air trapped in hairs surrounding their book lungs as a physical gill.

However, they do not have book lungs as most of their closest relatives, the spiders, do.

Often it lodges near a book lung, where it may remain for years before completing its development.

The respiratory system consists only of book lungs, which could be a reason why these spiders show a quite low level of activity.

On the ventral side of the abdomen are two hardened plates covering the book lungs.

Spiders have developed several different respiratory anatomies, based on book lungs, a tracheal system, or both.

They possess a second pair of book lungs, which appear as light patches behind the genital furrow.

Book lungs are not related to the lungs of modern land-dwelling vertebrates.

"We don't know anything about air conditions on the far side except that the bugs have book lungs, so thereis air.

Unlike many other arachnids, ricinuleids have no book lungs, and gas exchange takes place through trachea.

In all types of tarantula there are two sets of book lungs (breathing organs).

These may be trachea (tubes), or a modification of gills into a 'book lung'.

Scientists think book lungs evolved from book gills.

The book lungs look scarred; I'd say that this thing is extremely sensitive to additional oxygen and that's what killed it but it's just a guess.

Many arachnids have book lungs.

Mantispids that board spiders usually adopt positions on or near the base of the abdomen; some species may enter the spider's book lungs.

The blood of many spiders that have book lungs contains the respiratory pigment hemocyanin to make oxygen transport more efficient.