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.
Option (b) Pseudocoelomate
When body cavity is not completely lined by the mesoderm instead it is present in the form of scattered pouches, in between ectoderm and endoderm, this type of body, cavity called pseudocoelomate, e.g., roundworm.
Acoelomates the animals in which coelom is completely absent as, e.g., flatworms. e.g., annelids, molluscs, arthropods, etc.
Haemocoelomates are the animals in which body cavity is filled with haemplymph, e.g., arthropods, molluscs.