Cephalothorax vs Abdomen
The differentiation of body parts to be responsible for different functions has been a key component in the evolution of the animal kingdom, and segmentation of worm-like bodies was the first of that kind. Segmented worms have been evolved from roundworms and arthropods were given rise from segmented worms with additional modifications in their body structures. The cephalization and the segmentation underwent improvements with the formation of cephalothorax and abdomen. Since these are two differentiated regions of the arthropod bodies, there are many differences between cephalothorax and abdomen with respect to their form and function. Abdomen is a region of the body in most of the animals but, in order to compare it with the cephalothorax, this article mainly concentrates on the arthropod abdomen.
The two words cephalic and thoracic have been put together to mean both head and thorax with the term cephalothorax. Cephalothorax is simply the region of the arthropod body that comprises the organs and systems of both head and thorax. Chelicerates and crustaceans are the main arthropod groups with the fusion of head and thorax into one unit while the cephalothorax is not present in other groups such as insects. Tagmatization is the process forms the cephalothorax, which is located at the anterior end of the body; hence, it is aptly named as the Prosoma (anterior body). The prosoma could be observed from the exterior, as the arthropod external skeleton demarcates the region. Most of the sensory organs, mouthparts, and locomotion appendages are prominent in the cephalothorax. Usually, the cephalothorax is covered with a harder cuticle than the rest of the body, which makes it a rigid structure. The external structure that covers this region is called the carapace in crustaceans.
Abdomen is one of the main regions of the body that is located at the posterior to the thorax, and it is present in all the animals evolved after annelids and arthropods. Based on the location of the region, abdomen is also known as the opisthosoma, meaning the posterior body. Abdomen is composed of eleven segments, but one of those segments will be lost when they mature. However, there are only seven visible abdominal segments in honeybees and six in springtails. Some insects carry interesting features such as sting with barbs, which are useful in defending their enemies. Insects do not have locomotion appendages in the abdomen, but other arthropods viz. crustaceans do have legs in the abdomen. In insects, the abdomen is very distinctive, and that carries the reproductive and digestive organs mostly. In addition, the modification of respectively the first and second segments as the propodeum and petiole in ants is a considerable specialisation of the abdomen. The life is all about reproduction, and everything else is to support that function, abdomen is the region of the body containing those most important organs. Therefore, it could be envisaged that abdomen consists the most important and interesting organ systems of animals.
What is the difference between Cephalothorax and Abdomen?
• Cephalothorax is present only in arthropods while abdomen is common among most of other animal phyla.
• The cuticle is harder in cephalothorax than in abdomen. Therefore, the abdomen is flexible and tender while the cephalothorax in rigid and strong.
• Cephalothorax contains the sensory, feeding, and locomotion organs; however, the reproductive and digestive systems are based in the abdomen.
• Cephalothorax is an anterior region while the cephalothorax is a posterior region of the body.
• Cephalothorax is a fusion of two main body regions, whereas the abdomen is one distinctive region.