Ctenidia is found in the order

Answer: Option B

Ctenidia is found in the order Siphonoptera.
The order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds.
A ctenidium is shaped like a comb or a feather, with a central part from which many filaments or plate-like structures protrude, lined up in a row. It hangs into the mantle cavity and increases the area available for gas exchange.