Anatomy and Physiology:

All spiders have a very similar body plan, and when it comes to Phoneutria fera, things don’t differ too much. They are all broken up into two main segments; they include the prosoma or the cephalothorax, and the opisthosoma or the abdomen. These two segments are held together by a structure called the pedicle. The prosoma is the “head” region of the spider and contains all eight legs, the eyes, the chelicera, pedipalps and others. The opisthosoma then contains the spinnerets, anal opening, “lungs”, heart, and reproductive organs. This page will break each section down both internally and externally as well.

External: Perhaps the most obvious external feature on the cephalothorax are the eight jointed appendages or legs. The big powerful legs which are moved with striated skeletal muscles are the sole means of locomotion for all spiders. These legs are jointed in either four or five joints which all allow for movement only in one plane, similar to that of an elbow. The joint that connects the legs to the cephalothorax allow for circular movement similar to that of a shoulder or hip joint. The first and fourth legs will be the longer of the four and will be almost identical in their anatomy whereas the second and third legs will be shorter and be identical as well. The legs are also covered in what appear to be very short hairs. These hairs are actually receptors that are very sensitive and can even sense changes in air pressure. This will help them find a butterfly fluttering through the air or help them avoid the buzzing wings of their one main predator: The Tarantula Hawks.

     The next external parts of the cephalothorax are the chelicerae.  The chelicerae are the first appendages on the prosoma region and on P. fera are a noticeable red color. The chelicerae are found right under the eyes and are composed of two parts: the basal stout portion, and then the movable fangs which are located underneath. The fangs are used for injecting venom or injuring prey, cutting their silk threads (which is why the underside of the fangs are serrated), and even grasping objects, hence the chelicerae sometimes being referred to as the spider’s hands.

    Inside or underneath the chelicerae lie the Pedipalps or mouth parts. These are the second set of appendages and serve two main purposes. The first is to serve as copulatory organs and are used in the mating rituals of many spiders and the second is to move and manipulate the prey of the spider as they are eating it.

Internal: Although the Eyes can be seen externally, most of the eye lies beneath the exoskeleton. P. fera has eight eyes arranged in three rows. The first row has two(which are the most functional and useful for the spider), the second row has four, and the third row has two eyes that are widely spaced from each other. Each eye is connected to the main cephalized ganglion, or “brain”, which can be found on the ventral side of the cephalothorax.

    The first part of the Intestine is also found within the cephalothorax and extends from the mouth to through the pedicle into the abdomen. The main muscle found within the head region is the levator, or pharynx muscle, which controls the mouth parts of the spider. As stated before there exists a main ganglion found internally on the ventral side of the spider that serves as its brain.
Pedicle: this term simply refers to the thin waist like region of the spider that attaches the cephalothorax to the abdomen. This structure contains the aorta connecting the heart in the abdomen to the cephalothorax, a large nerve that connects the two segments, and the intestine which carries food brought in through the mouth on the cephalothorax to the midgut which is in the abdomen.

External: The abdomen is fairly limited in regards to its external anatomy. The main structures that are found externally on the abdomen are the spinnerets which are used for spinning the web and are located right below the anal opening. There are three pairs of spinnerets which are all highly coordinated because of the need for them to work individually as well as with one another to successfully spin their thread.

    Above the spinnerets is the anal opening which is used to secrete digested waste. The final external feature on the abdomen is the reproductive opening which is located on the ventral side of the spider. In males this is where the sperm will leave the body to fertilize the females. In females this is where the sperm will enter and fertilize the eggs and also where the fertilized eggs will leave the body.

Internal: The abdomen houses a variety of vital organs to the spider. The heart lies dorsally along the length of the abdomen. Spiders have a special form of heart known as a tube heart which is just as it is named. A muscular tube that helps to pump the circulatory fluid throughout the spider. Spiders have what is known as a open circulatory system which is characterized by a lack of closed veins and arteries. When the heart beats the circulatory fluid known as hemolymph is pushed through the arteries and veins into the various sinuses of the body.

    Located on the ventral side of the heart is the Midgut and Malpighian Tubules. The midgut brings in food from the intestinal tract and is attached to several malpighian tubules. The malpighian tubules brings the nutrients the spider needs from the midgut to the various parts of the spider which need these nutrients.

    The main means of respiration are also found internally on the abdomen and are referred to as the Book Lungs. These "lungs" differ greatly from those found in mammals. These lungs are found on the ventral side of the spider and look similar to a book by how they appear to be “pages” of air pockets which are used for gas exchange and to oxygenate the hemolymph that the atmospheric oxygen comes in contact with. The book lungs are connected to the heart so that the new oxygen rich hemolymph can immediately be pumped throughout the body. Book lungs more resemble gills than they actually do lungs.

    The final major abdominal internal structures are the spinning glands which are responsible for making the material that is used to spin webs which connected to and excreted out of the spinnerets.

Venom: The venom utilized by P. fera is widely considered as the deadliest in the world however certain components of that same venom are being researched for their use in the pharmaceutical field. First we’ll discuss the deadly part of the venom known as PhTx3. This toxin is a deadly neurotoxin that inhibits calcium ion channels in the nervous system leading to paralysis, but also has a powerful stimulating effect on serotonin receptors on nerves throughout the body which causes a great amount of pain. PhTx3 is known as a broad-spectrum calcium ion channel blocker which interferes with the part of the nervous system that is responsible for muscle contraction. If enough of the venom is injected into the victim full on paralysis will occur including paralysis of the diaphragm causing the victim to die of suffocation. The other components of the venom which are both problematic yet hopeful are the chemicals PhTx2-6. When enough of this toxin is injected into a mammal a condition known as priapism, painful penile erections lasting several hours, can occur. This chemical is currently being researched as a treatment for erectile dysfunction. This chemical differs from the functional chemical found in Viagra and other popular erectile dysfunction medications which has pharmaceutical companies racing to get this chemical into a functional drug that will help humans instead of paralyzing and killing them.

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