Body cavity is the cavity present between body wall and gut wall. In some animals the body cavity is not lined by mesoderm. Such animals are called A. Acoelomate B. Pseudocoelomate C. Coelomate D. Haemocoelomate
Hint:-The coelom refers to one of the characteristic features of metazoans. The coelom can be defined as a body cavity which produced during embryo development from the three germinal layers. The coelom is lined by mesodermal epithelium cells.
Complete answer:- There is a body cavity that presents between the alimentary canal and the body wall and is filled with fluid. This body cavity is known as a coelom. A true coelom mainly originated from a mesodermal. It is lined by mesoderm. At the time of the development of the embryo, the formation of coelom starts in the gastrulation stage of the embryo. The developing digestive tube of an embryo builds as a blind pouch which is known as the archenteron. Based on the presence of the coelom, there are three types of structural body formation found in animals which are Acoelomate, Pseudocoelomate, and Coelomate. In the case of the acoelomate, the body cavity or coelom is completely absent in these animals. Here, the blastocoel is completely occupied by mesoderm. In the case of the pseudocoelomate, no true coelom is present and the blastocoel is partly filled by mesodermal cells. In these types of animals, the body cavity is not lined by mesoderm. In that case, the mesoderm is found distributed between the ectoderm and endoderm. The body cavity of these animals is directly attached to the archenteron. This type of body cavity is called pseudocoelom which is derived from blastocoel. Aschelminthes i.e. Ascaris belongs to the pseudocoelomate. In the case of the coelomate, the animals possess a true coelom, and the coelom is lined by mesoderm on both sides, towards the body wall, and towards the gut. In this type of animal, the blastocoel found in the gastrula gets completely replaced by a true coelom. The body organs are suspended in the coelom by mesenteries. The phylum Annelida to Chordata are examples of this coelomate. Thus, the right option is B.
Note:- The coelom can be defined as a body cavity that presents between the alimentary canal and the body wall and is filled with fluid. The formation of coelom starts in the gastrulation stage during the development of the embryo. In acoelomate, the coelom is absent while in the pseudocoelomate, there no true coelom is present and the body cavity is not lined by mesoderm. And in the coelomate animals possess a true coelom.