Tarantula: Anatomy

Summary: Tarantulas are a frequently misunderstood animal so join Kiersten as she illuminates what makes them so cool! We start off with anatomy.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean.

 

Show notes: 

The Tarantula Scientist by Sy Montgomery

https://study.com/academy/lesson/tarantulas-anatomy-habitat-bite.html

https://www.britannica.com/science/book-lung

https://www.tarantulasdemexico.com/en/anatomia_en.htm

 

Transcript

(Piano music plays)

Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

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Kiersten - Welcome to Ten Things I Like About… This is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

 

My name is Kiersten and I have a Master’s Degree in Animal Behavior and did my thesis on the breeding behavior of the Tri-colored bat. I was a zookeeper for many years and have worked with all sorts of animals from Aba Aba fish to tigers to ravens to domesticated dogs and so many more in between. Many of those years were spent in education programs and the most important lesson I learned was that the more information someone has about a particular animal the less they fear them. The less they fear them the more they crave information about them and before you know it you’ve become an advocate for that misunderstood animal.

 

This is the first episode of tarantulas, my first misunderstood animal, and my first favorite thing about tarantulas is their anatomy! I’m not kidding listeners! This is one fascinating animal and o ne of the best ways to get comfortable with a misunderstood animal is to understand how they work, so let’s get started with the tarantula’s anatomy.

 

Tarantulas are classified as arachnids which means they are invertebrates that have eight legs. This puts them in the company of spiders, scorpions, harvestmen, ticks, and mites. Many people clump spiders and tarantulas together, but spiders and tarantulas are classified separately by scientists because of some anatomical differences and we’ll touch on these toward the end of this episode.

 

As invertebrates, tarantulas have an exoskeleton. This is a hard outer shell made of chitin that gives their body shape. To grow they must shed this exoskeleton periodically in a process called molting.

 

The most iconic attribute of tarantulas is their hair. This may be the biggest reason they creep people out, but this hair is super cool. The bristles are not made of of the same thing animal hair is made out, so technically not hair. Tarantula bristles are made of chitin, the same thing their exoskeleton is made of and there are four types of bristles. One type is the setae which all tarantulas have and these bristles act as sensory organs detecting chemicals, feeling vibrations, and sensing wind direction. The next type of bristles are the scopulae. These are found at the end of their legs and allow tarantulas to cling to surfaces. There are two other types of bristles that some but not all, tarantulas have, both are used in defense. One is the stridulating bristles that tarantula can rub together to make a hissing sound when threatened! How cool is that! And the fourth bristle is the urticating bristles that    can be detached from the abdomen and thrown at predators. These bristles are itchy and can irritate the nose, eyes, and mouth of a predator for hours.

 

Starting with the easily seen anatomy, tarantulas have two segments of their body the prosoma and the opisthosoma. The prosoma is the front portion of the tarantula, also known as the cephalothorax, where the eight legs are attached, where the eyes and mouth sit, and where the pedipalps attach. The opisthosoma is the back portion of the tarantula, often called the abdomen, where the lungs are housed and the spinnerets are attached.

 

Let’s take a closer look at the prosoma. The most notable appendage attached to the prosoma are the legs. Tarantulas have eight legs with seven segments on each leg. At the end of the legs are small tarsal claws that aide the tarantula in climbing and sticking to surfaces. These claws are retractable which means they can be extended when in use or brought back in when not in use. Depending on the species, there are two to three tarsal claws. 

 

Pedipalps are the second most obvious appendage attached to the prosoma. These are leg-like appendage at the front of the prosoma. They are often mistaken for legs but pedipalps are used to help catch and hold food, smelling, and feeling vibrations. They do not help the tarantula walk. Males will also use these to transfer sperm to the female during breeding season.

 

  The chelicerae are also on the prosoma but these are not as obvious unless you are holding the tarantula upside down, which I would not recommend, they really don't like that! The chelicerae kind of look like hairy beaver teeth and house the fangs and venom glands. They are also important in chewing their food. This chelicerae are so strong that they can sometimes use them to help move dirt in a burrow or even break roots that may get in their way. Another use for the chelicerae is for grooming. Tarantulas are very tidy and clean animals that use their chelicera, or mouth parts,   to groom their pedipalps and legs.

 

The eyes, eight of them are also found on the prosoma of the tarantula. They are located on the top, front portion of the prosoma just in front of the fovea, a depression in the middle of the carapace which the top of the prosoma. Tarantula eyes are mainly used for judging brightness of light rather than clear visual images. 

 

The prosoma also houses internal organs vital to the tarantula’s survival. As we covered before, the mouth is found here and the mouth leads to the esophagus and the stomach. The stomach is kinda like a vacuum, sucking food through the mouth and the esophagus. The underside of the fovea is where the suction muscles of the stomach are attached. 

 

The tarantula’s brain is also housed here in the prosoma. Their brain is definitely different from mammalian brains but it is just as important in processing environmental information. Their brain is divided into two ganglia, or bundles of nerves, that control nerve channels throughout the entire body. 

 

There are also large retractor muscles housed in the prosoma and these help anchor and control the mobility of the legs. These muscles are also anchored to the fovea just like the stomach muscles.

 

Alright, let’s move on to the second section of the tarantula’s body, the opisthosoma, or the abdomen. This is often the largest portion of the tarantula’s body. On the outside, the spinnerets poke out the back and these four appendages help produce and spin silk. 

 

There are four openings on the opisthosoma that connect to the tarantulas lungs, allowing oxygen transfer. And the anus is also found on this structure, because everyone poops!

 

Okay, let’s go inside the opisthosoma. Inside we run into the intestines. The glands that help produce silk are also found here. If it is a female tarantula her ovaries are housed in the opisthosoma. Last but defiantly not least, the lungs and heart are found here as well.

 

Now the tarantula has some of the coolest lungs around. They are called book lungs. Why? Because they look like the pages of a book. This is an old style of lung that does not expand and contact like our lungs. It’s actually a series of thin plates that are highly vascular and the entire surface area of the plates can transfer oxygen and carbon dioxide. This is where the slits in the opisthosoma become important. These slits allow the oxygen in and the carbon dioxide out.

 

Now these lungs are highly reliant on the pumping of the heart. The heart moves the hemolymph throughout the body of the tarantula. Hemolymph is the tarantula’s equivalent of mammalian blood, but the hemolymph does not stay in a maze of arteries and veins like our blood; instead, the heart pumps the hemolymph through arteries in the body that release the hemolymph directly into the body to oxygenate and feed the cells of the body. That’s why it looks all goopy when you squish a bug.

 

The tarantula relies on the thin plates of the book lungs being coated in hemolymph to help keep them oxygenated. It is incredibly important that both sections of the body get hemolymph and the pedicel is the structure that connects the prosoma to the opisthosoma. Sections of the heart, stomach and nervous system also run through the pedicel.

 

I know this a a lot of talk about tarantula anatomy, but I want to discuss one last really cool thing about their legs before I end this episode. The legs are all attached to the prosoma and every leg has about thirty muscles that move it, but the muscles can only retract the legs they cannot extend the legs.  We’ve all seen tarantulas walking, so how do they extend their legs? Their hemolymph! They rely on the pressure created by the hemolymph pumping through their body to extend their legs! How truly amazing is that!

 

In the beginning of this episode I said we’d talk about why scientists classify tarantulas and spiders in different families. Now that we’ve talked about their anatomy we can revisit this. There are two anatomical differences between tarantulas and other spiders, one is the book lungs. Tarantulas have book lungs while other spiders have more modern lungs. The second difference involves their mouth parts. Tarantulas can only move their mouth parts up and down while other spiders can move their mouth parts side to side. These two differences are significant enough to cause scientists to classify them in separate families. 

 

I hope you’ve enjoyed this look at tarantula anatomy because it is my first favorite thing about this misunderstood animal. 

 

If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change. 

(Piano Music plays) 

This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.