Basically its a closed loop of tubes, except for the muscular structure of the heart.
Circular structure.
A plasmid is a double stranded circular DNA
basin
Prokaryotes have circular DNA.
A host cell
Circular
The tympanic membrane.
a basin
No it is called the iris.
it represents the nucleus
A government structure that had the presidential assistants reporting start to the president on all issues.
Sand dollar's circular appearance is due to it's hard shell like structure called the Test that is circular. the test is covered by the spiny skin.