Jointed skeleton is absent in the

Explanation

In Biology, animals can have different types of skeletons, one of which is called a jointed skeleton. This type of skeleton is made up of segments that are connected by joints, allowing for flexibility and movement. The question is asking which animal does not have a jointed skeleton. Out of the options given, cockroach, spider, and millipede are all examples of animals that have jointed skeletons. However, snails do not have jointed skeletons, which is why option D is the correct answer. It is worth noting that snails have a hard external shell that protects their body, but this is not the same as a jointed skeleton. In fact, snails belong to a group of animals called mollusks, which have a different type of body structure compared to insects and arachnids. Understanding the different types of skeletons and body structures is important in Biology, as it helps us to classify and understand the diversity of animal life on Earth.