Q.Which one of the following organisms excrete waste through nephridia?

Before the vertebrate kidney evolved, animals used a range of simpler excretory arrangements that are still found today across the invertebrate world. Unicellular organisms rely on a contractile vacuole that periodically collects and discharges waste and excess water out of the cell. Sponges have no dedicated excretory organ; waste simply diffuses into the water current flowing through the body and exits via the osculum.

True excretory organs — a simple or branching tube opening to the exterior through a nephridiopore — appear once animals evolve bilateral symmetry. Two main types of nephridia exist: protonephridia, networks of dead-end tubules called flame cells, found in animals lacking a true body cavity (such as flatworms) and also in rotifers, some annelids and Amphioxus; and metanephridia, unbranched coiled tubes that collect body fluid through a funnel-shaped nephrostome and discharge it via the nephridiopore, as in earthworms. …