External Anatomy
Just like in other arachnids, the body of the scorpion is divided into two main segments: the prosoma (cephalothorax) and the opisthosoma (abdomen). The opisthosoma is then divided into the mesosoma (preabdomen) of seven segments, which contains most internal organs, and the metasoma (postabdomen) of five segments. Attached to the end of the metasoma is the telson, which contains the venom glands. On the end of the telson is the aculeus (stinger), which releases the venom.
On the anterior end of the prosoma are the median eyes, in the center of the carapace, and up to five pairs of smaller lateral eyes, which are on the sides. On the underside of the prosoma is the base of each coxa (appendage). Unlike in insects and crustaceans, the scorpions’ joint between the body and coxae is relatively immobile (Bowerman and Root 57). Extending out are four pairs of walking legs. The legs are divided into segments called the femur, patella, tibia, basitarsus, and tarsus. Leg length increases as you move from anterior to posterior (Bowerman and Root 57). The prosoma also bears the chelicerae, which are the mouthparts, and the pedipalps, which are large pincers. They are divided into segments called the femur, brachium, and chela. The chela has one fixed and one moveable finger.
The coxae surround a small plate called the sternum. Posterior to the sternum are segments called sternites. The first of which contains the genital operculum, which is a pair of plates covering the genital pore. Posterior to that, on the second segment, are the pectines. These are sensory organs unique to scorpions that aid in locating prey (Hjelle and Polis).
On the anterior end of the prosoma are the median eyes, in the center of the carapace, and up to five pairs of smaller lateral eyes, which are on the sides. On the underside of the prosoma is the base of each coxa (appendage). Unlike in insects and crustaceans, the scorpions’ joint between the body and coxae is relatively immobile (Bowerman and Root 57). Extending out are four pairs of walking legs. The legs are divided into segments called the femur, patella, tibia, basitarsus, and tarsus. Leg length increases as you move from anterior to posterior (Bowerman and Root 57). The prosoma also bears the chelicerae, which are the mouthparts, and the pedipalps, which are large pincers. They are divided into segments called the femur, brachium, and chela. The chela has one fixed and one moveable finger.
The coxae surround a small plate called the sternum. Posterior to the sternum are segments called sternites. The first of which contains the genital operculum, which is a pair of plates covering the genital pore. Posterior to that, on the second segment, are the pectines. These are sensory organs unique to scorpions that aid in locating prey (Hjelle and Polis).
Internal Anatomy
Attached to the inner wall of the cuticle are striated muscles. Their muscle strength comes from rapid impulse rate firing, rather than an increased number of fibers. They have fast (phasic) neurons for rapid movement and slow (tonic) neurons for slow movement. A tubular heart is located on the dorsal side and runs the entire length of the mesosoma. This pumps the colorless hemolymph through tiny arteries to each appendage as well as to the nerve cord before emptying into the hemocoel.
Scorpions have a central nervous system with a brain, composed of two large ganglia, and a ventral nerve cord. Their eyes cannot form sharp images, but are incredibly sensitive to light, allowing them to navigate at night. Some species also have light receptors in the tail. Chemoreceptors are located in the oral cavity and in the pectines for taste.
The digestive tract contains the mouth, pharynx, esophagus, and hepatopancreas, which contains the cecal glands, which produce digestive enzymes. The hepatopancreas is a large organ and constitutes about 20% of the total body mass. Also included are the midgut and the hindgut. Scorpions possess Malpighian tubules which filter nitrogenous waste.
The first four sternites contain a pair of spiracles, which are tiny pores that open up to the book lungs, the respiratory organs of the scorpion. These consist of a set of very thin membranes all placed together to resemble a book.
Reproductive organs include gonads, which are present in both males and females, seminal vesicles are possessed by males and eggs by the females (Encyclopedia Britannica).
Scorpions have a central nervous system with a brain, composed of two large ganglia, and a ventral nerve cord. Their eyes cannot form sharp images, but are incredibly sensitive to light, allowing them to navigate at night. Some species also have light receptors in the tail. Chemoreceptors are located in the oral cavity and in the pectines for taste.
The digestive tract contains the mouth, pharynx, esophagus, and hepatopancreas, which contains the cecal glands, which produce digestive enzymes. The hepatopancreas is a large organ and constitutes about 20% of the total body mass. Also included are the midgut and the hindgut. Scorpions possess Malpighian tubules which filter nitrogenous waste.
The first four sternites contain a pair of spiracles, which are tiny pores that open up to the book lungs, the respiratory organs of the scorpion. These consist of a set of very thin membranes all placed together to resemble a book.
Reproductive organs include gonads, which are present in both males and females, seminal vesicles are possessed by males and eggs by the females (Encyclopedia Britannica).