Spider Anatomy (Part II)

In the last article we have discussed the external parts of a spider's anatomy, comprising basically of the two segmented parts: The abdomen and the cephalothorax. In the previous article, the cephalothorax and its components were discussed and exemplified. In this article we will be discussing more about the abdomen part of the spider's anatomy as well as its internal parts and their function.

The Abdomen

Unlike the cephalothorax part of the spider, the abdomen is rather soft and saclike. Located in the underside of the spider's abdomen are actually three pairs of spinnerets. Spinnerets are actually where a spider's thread comes out. It serves as an outlet for the silk producing glands that a spider has. Each of the three spinnerets produces different quality of spider silk with each other but contributes in a diversified function whether for creating an orb web or capturing their prey. They are also studded with fine, hair-like cylinders or tubes called spigots, which are the ones responsible for creating different types of spider silk threads. The spigot tubes actually lead to the different types of silk glands that spider's abdomen has. Inside the abdominal glands, silk is initially produced as liquid. When the spigots shoots the silk liquid, certain protein molecules and components of the silk will line up with one another causing the entire material to harden once it hits air. The silk then forms into a s
trong, highly elastic fiber filaments which the spiders use as well for all of its locomotion.

However, the air is not the responsible factor as to why the silk harden once it comes out of the spider's body. It is the process of which the spigots draw them out of the spider's silk producing glands. The silk produced by the different spigots may combine and fuse altogether to form a much more elastic and stronger silk fiber or filament. The spinnerets of a spider is not actually just mere punctures in the spider's abdomen, but are regarded by most scientists as a spider's hidden limbs. It is considered so because spinnerets can move accordingly as to how the spider would be using its silk, whether by capturing a prey or creating its dwelling. This is also the reason why a marvel concept character, Spiderman, shoots his threads out of his hands instead of his ass. Apart from the fact that it would utterly ridiculous if Spiderman would shoot webs from the behind, it is also essentially because of the truth that spider's spinnerets are actually their hidden limbs.

Internal Anatomy

Have you ever squished a spider? Have you ever tried paying attention to what you have just crushed? If so, you would have noticed that once you squish a spider, it's just their blood that you see and certain bodily fluids colored grey or ash and sometimes with something white.

You may have thought that a spider doesn't have any sort of insides in them; and that they are all made of liquid and mushy flesh parts and its only their exoskeletons that's making them as hard as they can. However, you are truly wrong if this is what you think about a spider's inside. Because like it or not, a spider's body interior is comprised of a lot of things as well, including a nervous system. You better think twice again when you are squishing off spiders mercilessly. Think about the amount of excruciating pain they would have to go through to die at your whim.

The cephalothorax part of the spider's anatomy is actually a shell casing to a lot of the spider's interior parts. In the cephalothorax resides the spider's digestive system and nervous system. The abdomen of a spider is also the place where most of the vital organs of a spider are located. Vital organs such as a long, tubular heart, reproductive organs, excretory organs and respiratory organs are all found in a spider's abdomen.

The Respiratory System

A spider actually has two types of respiratory organs. One type of breathing organ is the book lungs and the other is the tracheal tube. There are certain narrow slits within the abdomen of a spider and they are leading to two to four respiratory organs namely, book lungs. They are named that way because of their alternating levels or layers of air spaces certain minute leaflets all filled with their blood, making it look something like of an open book. Each time the spider breathes, the oxygen in the air would immediately be sifted through the very thin cuticle leaflets and right into the blood of the spider.

There are also small openings located nearby the spinnerets. However, they are not in any way related to the silk production process of the spider. These holes are called spiracles and leads to the cuticle-made tracheal tubes. These almost microscopic tubes are allocated all over the body to distribute air to the spider's entire system.

Blood Circulation

A spider's blood is not red. If you have squished spiders from time to time in your life, you would have known this by now. Their blood is actually called hemolymph. The hemolymph contains lots of blood cells and oxygen delivering blood pigments called hemocyanin. Hemocyanin is also the responsible component why a spider's blood is colored grey or light blue. In contrast to the humans blood with blood cells containing haemoglobin which carries the oxygen all throughout the human body, a spider's blood has also an almost the same characteristics. It also have blood cells that carry oxygen to the many different parts of a spider's anatomy, as well as certain antibodies that help combat harmful bacteria to a spider and as well wound recoveries.

Unlike humans with an apparently mango-shaped hearts, a spider's heart is rather cylindrical or tubular in shape and it lies in the back part of the abdomen. Each time it contracts it delivers the blood forward into the cephalothorax then sends it back to the abdomen. Blood would travel into very small tubes or also called arteries which are vastly distributed in their entire body cavity.