Question

Coelom is lined on all sides by
A. Endoderm
B. Ectoderm
C. Mesoderm
D. Ectoderm and Endoderm

Answer 1

Hint: Ectoderm, Endoderm and Mesoderm are the germ layers formed during the embryo formation. These layers give rise to tissue/organ present in the body of an organism.

Complete answer:
Depending upon the number of germ layers in the embryo, animals divided into two categories:
Diploblastic: Those animals in which the developing embryo has only two germinal layers, i.e., an external layer ectoderm and an internal layer endoderm. The undifferentiated layer called mesoglea is present between the ectoderm and endoderm and mesoglea is not specialized to form any particular tissue/organ of the body. e.g., Coelenterates and Ctenophores.

Triploblastic: Those animals which have three germinal layers in the developing embryo, i.e., ectoderm, mesoderm and endoderm. The mesoderm is present in between the ectoderm and endoderm. e.g., Platyhelminthes to chordates (all animals are triploblastic).
Coelom or true body cavity refers to a large fluid filled space (cavity) lying between the outer body wall and inner gut wall. The Coelom contains most of the visceral organs and is lined by mesoderm on all sides.
Animals can be divided into three types on the basis of absence or presence of Coelom in the body:
Eucoelomate: The true Coelom is a body cavity which arises as a cavity in embryonic mesoderm. The Coelom is filled with coelomic fluid secreted by peritoneum. e.g., Annelids, echinoderms and chordates.
Pseudocoelomates: The Coelom is present but it is not perfectly lined by mesoderm and the animals known as Pseudocoelomates. e.g., Aschelminthes.
Acoelomates: The Coelom is absent in these types of animals. e.g., Sponges, ctenophores, coelenterates and Platyhelminthes.

So the correct answer is option C.

Note: Schizocoelom (annelids, arthropods and molluscs) and Enterocoelom (echinoderms and chordates) are the subcategories of Eucoelomate. Body cavity of arthropods and non-cephalopod mollusks is called haemocoel.