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The Development of Chondrocranium of Chondrichthyes Essay

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Chondrichthyes possess a skeleton that differs considerably from other species in that their skeletons are made up of cartilage rather than bone. This project gives insight on the normal developmental pattern of the chondrocranium of a chondrichthyan, using the little skate, Leucoraja erinacea as a model organism. This is demonstrated by using histological techniques to visualize and describe this sequence of chondrocranium development, focusing on two stages of development. In the context of what is morphologically known from their relative taxas and other chondrichthyans, the developmental pattern that occurs in these two stages is given in detail. It’s suggested that from anterior to posterior, beginning with the earlier of the two…show more content…
Starting off as a pair of parachordal cartilage, the basal region, or basal plate will grow to surround the notochord and pair with prechordal cartilages, the trabeculae cranii, that form in front of the notochord to form the ethmoid plate. The occipital region will form at the posterior end of the chondrocranium and surround the descending notochord via a segmented occipital arch, which exhibits similarly to that of a vertebral column present in vertebrates having both a neural and hemal arch (3).
The little skate, Leucoraja erinacea, is a chondrichthyan that is a key model organism for chondrichthyan embryology studies. As an oviparous species, after internal fertilization its development is independent of its mother, encapsulated in a laid, moderately thin keratinized egg case during embryonic development. These embryos receive nourishment via a yolk sac located in the egg case and remain capsuled during development for approximately 6-9 months (Figure 2a-j). As an oviparous species, they are amenable to experimental embryological manipulation and therefore are important as a model organism.
Chrondrichthyans are an important lineage in that their studies can shed light onto evolutionary processes that can give key insights into both development of extinct early-jawed fishes and the evolution of higher
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