Planarians Lack Dedicated Respiratory and Circulatory Systems

Multiple Choice

Planarians lack dedicated respiratory and circulatory systems. This deficiency does not cause a problem because ________.

A) none of their cells are far removed from the gastrovascular cavity or from the external environment
B) they lack mesoderm as embryos and, therefore, lack the adult tissues derived from mesoderm
C) their flame bulbs can carry out respiratory and circulatory functions
D) their body cavity, a pseudocoelom, carries out these functions