Book Lungs

Tarantulas breath only by using book lungs.  Here, oxygen diffuses into the blood stream with membranous tissue arranged in folds that closely resemble the leaves of a book.

Heart 

The heart is located in the tarantulas abdomen near the top. The heart is long and slender and pumps blood through the tarantula. Tarantulas have a open circulatory system which simply means that blood fills the entire body cavity.  This is much like water in a water tank. 

Nervous System

The nervous system is located in the chelicerae and consists of two clusters of nerve ganglia, which form the tarantulas central nervous system.  Nerves then branch out from this control center and are distributed throughout the tarantulas body.

Digestive Tract

Tarantulas have a rather unique digestive tract. Since they do not have the ability to digest solid food, they must first digest the food externally and consume it as a liquid. To accomplish this, tarantulas have an esophagus, midgut, sucking stomach, and excretory organs. 

Silk Glands

Most tarantulas have at least 3 silk glands that reside in their abdomen.  While in the silk glands, the silk is in a liquid form.  Only when it is excreted through the spinnerets does it turn to a solid. 

Unlike other spiders, tarantulas do not hang from their webs.  Tarantulas primarily use their webs to construct burrows and to wrap uneaten food remains.