Tarantula Anatomy and Behavior

Classifying tarantulas (Family Theraphosidae) requires extensive knowledge of their external morphology, which studies the form of an organism by looking at the parts of its body. Knowing the location and function of each part of a tarantula's body makes it easier to study and understand them, even when not trying to perform scientific classification. This diagram outlines the anatomy of a tarantula.

Tarantula Anatomy Diagram

1. Opisthosoma: One of two main parts of a tarantula's anatomy and the rear section of the body, often referred to as the abdomen. The opisthosoma houses the two pairs of book lungs, a primitive respiratory system consisting of ventilated, leaf-like lungs through which air circulates. It also internally contains the heart, reproductive organs, and the midgut. The spinnerets can be found externally on this part of the tarantula's body. The opisthosoma can expand and contract to take in nutrients or expel eggs.
2. Prosoma: The other main part of a tarantula's anatomy, or front section of the body that is often called the cephalothorax. The dorsal surface of the prosoma is protected by the carapace. The legs, fangs, and pedipalps all extend from the prosoma region externally. Internally, you will find the tarantula's brain, a network of muscles responsible for much of a tarantula's movement, digestive organs, and venom glands.
3. Pedicel: An hour-glass shaped tube that joins the two primary body sections, the exoskeleton or prosoma to the abdomen or opisthosoma. The pedicel contains many nerves and blood vessels internally.
4. Carapace: A very hard, shield-like plate that covers the dorsal surface of the prosoma region. The carapace has many functions. It houses the eyes and fovea, but it is also responsible for protecting the top of the cephalothorax. The carapace is a crucial part of the exoskeleton of a tarantula and its covering of hairs also functions as an effective defense mechanism.
5. Fovea: A dimple on the dorsal surface of the prosoma, or more specifically, the carapace. Many of a tarantula's muscles are fixed to this important feature, including its stomach muscles. The fovea is also called the foveal groove. Its size and shape determine how the tarantula's limbs will move.
6. Ocular tubercle: A small mound on the dorsal surface of the prosoma which holds the tarantula's eyes. This bump is located on the rigid carapace. Tarantulas usually have eight eyes. Though famously ineffective for vision, tarantula eyes may help them to calculate distance or take in polarized light.
7. Chelicerae: Jaws or system of mouthparts that house the venom glands and fangs, which are used for envenoming prey. These are fastened on the front of the prosoma and are quite large. Tarantulas primarily use their chelicerae for eating and hunting.
8. Pedipalps: Sensory appendages. Although they resemble shorter legs, pedipalps are just designed to help tarantulas to feel their environment. The pedipalps usually have only one claw each, compared to their true legs that each contain two claws. In males, the pedipalps are also used for sperm transfer.
9. Legs: A tarantula's true legs each have two claws on the tarsus (foot). Setae, or the coarse hairs also covering the carapace, can be found on each of the legs and these also help the tarantula to feel their environment and sense danger or prey. A tarantula has four pairs of two legs, or eight legs total, containing seven segments each.
10. Spinnerets: Silk-producing structures. Tarantulas have two pairs of these appendages and they extend mostly into the abdomen. Tarantulas use silk to defend themselves against threats and create webs for shelter.

Sources

• Anatomy, Theraphosidea website by Dennis Van Vlierberghe. Accessed online September 11, 2019.
• The Tarantula Keeper's Guide: Comprehensive Information on Care, Housing, and Feeding, by Stanley A. Schultz, Marguerite J. Schultz
• The Natural History of Tarantulas, British Tarantula Society website. Accessed online December 27, 2013.