Spider Anatomy – A quick introduction

Anatomical features of can be used as identification of spiders. Here follows a quick overview.

Overall, the body parts of a spider can be divided into two main parts: The prosoma, or cephalothorax, which forms the head region of the spider and the opisthosoma, or abdomen, which forms the lower part. In this post, I will try to give you a quick overview of nearly all visible parts of a spider.

The primary parts of a spider

The prosoma, also known as the “cephalothorax”, contains all motoric parts of the spider (Paul et al., 1989). This includes the mouthparts, the pedipalps, the eyes and thus also the “brain” of the spider, as well as its eight legs.

The prosoma is protected from above and below by a layer of chitin, where the upper layer is referred to as the “carapace” and the lower layer is called “strenum”. The pleura is a slightly elastic skin connecting carapace with strenum (bioportal, 2024).

The opisthosoma, or simply “abdomen”, makes up the primary mass of the spider and includes all other vital organs (Paul et al., 1989). This part is not protected by an additional chitin layer, resulting in slight elasticity and is therefore very sensitive to pressure (“Spider Ecophysiology”, 2013).

The Spider’s Prosoma

The legs. A spider usually has eight legs. However, in the event of an attack, it can get rid off an endangered leg. “Better to loose my leg than my life!”, so the spider. If our eight-legged friend has gone through its last moult, the lost leg can be regenerated (C. Kropf & H. Frick, 2024).

A spider leg can be divided into seven segments (as shown in the picture). These segments are each separated by a joint.

At the end of each tarsus there sits a tarsal claw. Interestingly, orb-weaving spiders often have an additional claw on their tarsi. It is assumed that this addition helps them with the construction of their orb-web (C. Kropf & H. Frick, 2024).

Spider Eyes. Many people know that spiders have several eyes. These eyes have been evolved in a way to support the different lifestyles araneomorph spiders.

The position and size, as well as the overall existence of particular eyes, can thus be used to include or exclude certain families of spiders within the order of araneomorphs.

Learn more:
Orders and suborders of spiders

Although most spiders have quite a number of eyes, this sensory organ is by far not the most important one. Interestingly, most web-building spiders would only be see clearly through glasses (F. Barth, 2001).

Fangs and chelicerae. The chelicerae are the primary mouthparts of a spider. Each equipped with a fang, these tiny weapons are used to inject poison into caputred prey. The administration of venom through the use of fangs is a typical for spiders.

But beware: Spiders of the family Uloboridae do not have venom glands and can, therefore, not administer any poison (C. Kropf & H. Frick, 2024). Isn’t that amazing?

The pedipalps. The first leg-like extremities besides the chelicerae are not feet, but pedipalps. The tarsi of those weirdly shaped leg-like appendages differ in structure and appearance between the sexes and can thus be used to identify the gender of a spider.

While female pedipalps resemble their other legs, but are smaller in appearance, male pedipalps are a vital copulatory organ. Male palps are thus often used to not only identify the gender, but the specific species of a spider.

The male palp is formed to fit perfectly with the female genitalia. Therefore, almost all spiders can be identified by examining their respective copulatory organs. (Kropf & Frick, 2024).

The Spider’s opisthosoma

The spinnerets. The spinning apparatus of a spider consists of several spinnerets, where the number and distribution varies between spiders. Each spinneret enables the spider to spin different types of silk. The well-known common garden cross spider (Araneus diadematus) uses up to seven different silks in its lifetime (C. Kropf & H. Frick, 2024).

Respiration. Spiders of the suborders Mesothelae and Mygalomorphae (tarantulas) each have two pairs of Book-lungs. Yes, lungs!

Read more:
The suborders of spiders

With the exception of members of the family Hypochilidae, all araneomorph spiders breathe with a combination of book lungs and tracheae. In some species, the tracheae are even the preferred respiratory system (Spider Ecophysiology, 2013).

Sources

• Images: All images are taken by the author N. Schneider.
• Paul, R., Tiling, K., Focke, P., & Linzen, B. (1989). Heart and circulatory functions in a spider (Eurypelma californicum): the effects of hydraulic force generation. Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, 158(6), 673–687. https://doi.org/10.1007/bf00693005
• C. Kropf & H. Frick. (2024). Spider Biology. Lecture UniBe, Switzerland.
• Spider Ecophysiology. (2013). In Springer eBooks. https://doi.org/10.1007/978-3-642-33989-9
• bioportal. Spider Anatomy Ontology (2024). [online] https://tinyurl.com/ynkfvfmm
• Barth, Friedrich G. (2001): Sinne und Verhalten: aus dem Leben einer Spinne, Springer eBooks, [online] doi:10.1007/978-3-642-56813-8.

Last updated: 02. January 2025