Planarians lack dedicated respiratory and circulatory systems 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.

Question

Quizplus · Accepted Answer

Planarians have a simple body structure with their cells not far removed from the gastrovascular cavity or the external environment. This makes it unnecessary for them to have dedicated respiratory and circulatory systems.

Planarians Lack Dedicated Respiratory and Circulatory Systems Because