What is the Difference Between Carapace and Plastron 

The main difference between carapace and plastron is that a carapace is a protective exoskeleton on the dorsal side, whereas a plastron is a protective shield on the ventral side.

The carapace and plastron are two parts of the exoskeleton of turtles and tortoises. Exoskeleton is a hard covering that protects and supports the body of animals.   

Key Areas Covered

1. What Carapace
– Definition, Structure, Importance
2. What is Plastron
– Definition, Structure, Importance
3. Similarities Between Carapace and Plastron
– Outline of Common Features
4. Difference Between Carapace and Plastron
– Comparison of Key Differences

Key Terms 

Carapace, Plastron

What is Carapace

The carapace is the dorsal part of the exoskeleton of turtles and tortoises. The carapace structure is made up of ossifying spine and ribs fused to the dermal bone. They ossify into dermal plates beneath the skin, forming a hard shell. A keel is present in some species of turtles. It is a ridge running from the front to the back. Single, paired, or three rows of keels can occur. However, the carapace is flat in most species of turtles. Also, the color of the carapace can vary among species. Especially in the leatherback sea turtles, pig-nose turtles, and soft-shell turtles have reduced ossification of the carapace. Also, they do not have scutes, but skin covers their shell. Additionally, these turtles are highly aquatic forms.

Figure 1: Exoskeleton of Turtle

Furthermore, scutes are the horny plates that cover the exterior of the skin of turtles. They are made up of keratin. Also, they protect the carapace from scrapes and bruises. Further, the scapula of turtles occurs inside the ribcage, while the scapula of other tetrapods occurs outside the ribcage. Also, the shells of other tetrapods do not directly attach to the vertebral column. Therefore, their ribs move freely, surrounding intercostal muscles. But turtles do not have intercostal muscles. 

What is Plastron

Plastron is a nearly flat shell structure of a turtle. Significantly, it occurs on the ventral surface of the turtle. Also, the plastron is made up of nine bones and two epiplastra. The anterior border of the plastron is homologous to the clavicles of other tetrapods. The other parts of the plastron are homologous to the gastralia of other tetrapods. Primarily, the plastron is developed from the sternum of the turtle. In the evolution, the sternum was repurposed into the plastron. Some turtles have a movable hinge between the pectoral and abdominal scutes to enclose themselves completely. In some species of turtles, the shape of the plastron differs in males and females. Their males have concave plastrons, while females have convex plastrons. It easily mounts the animal during copulation.

Figure 2: Plastron

Moreover, the relative lengths of the seam segments are important for the recognition of the species of the turtle. The joining of the plastral scutes in the middle of the plastron forms a central seam. Also, the plastron contains six lateral pairs that are symmetrical. They are gular, humeral, pectoral, abdominal, femoral, and anal pairs. The most anterior part of the plastron is the gular scute. Some turtles have paired gular scutes. Others have undivided, single-gular scutes.  

Similarities Between Carapace and Plastron

• The carapace and plastron are two parts of the exoskeleton of turtles and tortoises.
• They protect the body of these animals.
• They are bony structures. 

Difference Between Carapace and Plastron

Definition

Carapace refers to a bony or chitinous shield, test, or shell covering some or all of an animal’s dorsal part as a turtle. In contrast, plastron refers to the nearly flat part of the shell structure of a tortoise.

Occurrence

The carapace is the dorsal part of the exoskeleton, while the plastron is the ventral part of the exoskeleton. 

Shape

The carapace is convex, while the plastron is flat. 

Conclusion

In brief, carapace and plastron are two parts of the exoskeleton of turtles and tortoises. The carapace is the dorsal part of the exoskeleton, and it is convex. In comparison, the plastron is the flat ventral part of the exoskeleton. Therefore, the main difference between carapace and plastron is their occurrence and shape. 

References:

1. Wikimedia Foundation. (2023ab, July 22). Turtle Shell. Wikipedia. 

Image Courtesy:

1. “Turtle skeleton cross-section, labelled as infographic” By Ian Alexander – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “Painted Turtle’s Plastron “belly shell” By Ptarp – Own Work (CC-BY SA 3.0) via Commons Wikimedia