Question

Schizocoelomates and enterocoelomates are

A. Acoelomates

B. Invertebrates

C. True coelomates

D. Echinoderms only

Answer 1

Hint: Coelom is a fluid-filled cavity between the body wall and gut wall. It is lined by mesoderm. On the basis of the presence or absence of coelom, animals are classified into three groups, namely coelomates and pseudocoelomates and acoelomates. Coelomate animals possess coelom between the body wall and digestive tract.

Complete answer:

The presence or absence of coelom is an important basis of classifications in animals.

True body cavity; Coelomates (true body cavity) are those organisms in which the tissues derived from the mesoderm completely line the fluid filled body cavity while in pseudocoelomates (false body cavity) the mesodermal tissues do not completely line the fluid filled body cavity.

Generally, the true coelom is categorized into two types, one is schizocoelom and the other one is enterocoelom. This categorization is based on how a true body cavity or coelom arises in different animals. Based on the ways, the true body cavity or coelom arises in different animals.

Schizocoelom: Schizocoelomates are any invertebrate animal that possesses a schizocoel, a coelom (that is, the body cavity lying between the digestive tract and the musculature of the body wall) formed through the splitting of the mesodermal mass, the middle germ layer in embryonic development.

Enterocoelom: Enterocoelomate is any animal in which the mesoderm-lined body cavity (coelom) arises in the embryonic stage as an outpocketing of the developing gut (enteron). 

Hence, the correct answer is option C. Schizocoelomates and enterocoelomates are referred to as the true coelomates.

Note:

During the development of the embryo, a body cavity is formed from the three germinal layers resulting in formation of a body cavity or true coelom. Mesodermal epithelium cells line up the coelom. Based on the nature of coelom, the animals are divided into three groups:

Acoelomate: Coelom is absent. The blastocoel is completely occupied by mesoderm.

Pseudocoelomate: True coelom is not present. The blastocoel is partly filled by mesodermal cells. 

Eucoelomate: Animals that have a true coelom.