Final answer:
Sharks are part of the Chondrichthyes class, notable for their cartilaginous skeletons, versus the bony skeletons of Osteichthyes. They exhibit primitive vertebrate features and have a widespread evolutionary impact, showcasing significant traits such as a varying number of gill slits and fin types.
Step-by-step explanation:
Members of the class Chondrichthyes, such as sharks, differ from members of Osteichthyes by having a skeleton made of cartilage rather than bone. The spiny dogfish is a type of shark that would be categorized within Chondrichthyes. In the context of evolutionary biology, sharks are known to have branched off early in the vertebrate evolutionary tree. This is demonstrated by the fact that sharks like the wobbegong, with its distinguishing skin flaps and camouflage, have retained some of the more primitive features of early vertebrates, such as a large number of gill slits and variations in fin structures.
When considering analogies in evolutionary biology, the dolphin and fish share a convergent evolution that gives them similar body shapes due to their adaptations to aquatic environments, despite having branched off at different points in the animal phylogenetic tree. This type of similarity is referred to as analogous structures.
Regarding the skeletal system, animals such as arthropods possess an exoskeleton, which is a type of hard skeletal layer found on the exterior of the organism. In contrast, the classification of animals based on the number of embryonic tissue layers includes diploblasts and triploblastic with diploblasts generally displaying radial symmetry while triploblast have bilateral symmetry.