Spider anatomy

Overview of the anatomy of spiders

Spider anatomy refers to the structure and organization of the body of spiders, which are arachnids belonging to the order Araneae. Spiders are characterized by their two-part body structure, eight legs, and the ability to produce silk. This article provides an overview of the key anatomical features of spiders, including their external and internal structures.

External Anatomy

Spiders have a distinct body plan that is divided into two main parts: the cephalothorax and the abdomen.

Cephalothorax

The cephalothorax, also known as the prosoma, is the anterior part of the spider's body. It is a fusion of the head and thorax and houses several important structures:

• Eyes: Most spiders have eight simple eyes arranged in various patterns, although some species have fewer. The arrangement and number of eyes can help in identifying different spider families.
• Mouthparts: The chelicerae are the primary mouthparts, equipped with fangs that inject venom into prey. Behind the chelicerae are the pedipalps, which are sensory organs and, in males, are used in reproduction.
• Legs: Spiders have four pairs of legs attached to the cephalothorax. Each leg consists of seven segments: coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus.

Close-up of a spider's eyes

Abdomen

The abdomen, or opisthosoma, is the posterior part of the spider's body. It is soft and unsegmented, containing vital organs such as the heart, digestive system, and reproductive organs.

• Spinnerets: Located at the rear of the abdomen, spinnerets are silk-spinning organs. Spiders use silk for various purposes, including web construction, prey capture, and egg protection.
• Book lungs: These are respiratory organs found in the abdomen, consisting of stacked plates that facilitate gas exchange.

Internal Anatomy

The internal anatomy of spiders includes several specialized systems that support their predatory lifestyle.

Digestive System

Spiders have a unique digestive system adapted for their carnivorous diet. They inject digestive enzymes into their prey to liquefy the tissues, which are then sucked into the stomach.

Circulatory System

Spiders possess an open circulatory system with a heart located in the abdomen. Hemolymph, the spider's blood, is pumped through the body cavity, delivering nutrients and oxygen to tissues.

Nervous System

The nervous system of spiders is highly centralized, with a large ganglion in the cephalothorax that acts as a brain. This controls the spider's movements and sensory processing.

Reproductive System

Spiders exhibit sexual dimorphism, with males often being smaller than females. Males use their pedipalps to transfer sperm to the female's epigyne, a specialized structure on the abdomen.

Silk Production

Silk production is a defining feature of spiders. Silk is produced in specialized glands and extruded through the spinnerets. Different types of silk are used for various functions, such as building webs, creating egg sacs, and forming draglines.

Related Pages

• Arachnid
• Web (spider)
• Venom
• Predation