Question

Which of the following statements is incorrect?
A. In cockroaches and prawns excretion of waste material occurs through Malpighian tubules.
B. In ctenophores, locomotion is mediated by comb plates.
C. In Fasciola, flame cells take part in excretion.
D. Earthworms are hermaphrodites and yet cross-fertilization takes place among them.

Answer 1

Cockroaches are insects that excrete or remove waste from the body by tubular structures. Prawns are crustaceans and excrete through the green gland. Fasciola are parasitic trematodes like a liver fluke. Ctenophores are invertebrates including comb jellies. Hermaphrodites are animals that have both male and female organs in every individual body.

Complete answer: To find out which of the above-given options is incorrect, let us discuss each statement in detail.
Statement A says that in cockroaches and prawns the excretory organ is the same and that is Malpighian tubules. Excretion refers to waste removal from the body. Each organism has different organs and ways to remove waste. Cockroaches being an insect excrete using malpighian tubules. On the other hand, a prawn is a crustacean. It excretes using green glands that help in the removal of nitrogenous waste from its body. Thus, this statement is incorrect.
Statement B says that in ctenophores, locomotion is mediated with help of comb plates. The body of ctenophores bears eight rows of comb plates externally. These plates are lined with fine cilia or hair-like structures that mediate movement. The presence of cilia gives these plates a comb-like appearance. So, this statement is correct.
Statement C is that in Fasciola, flame cells take part in excretion. The flame cells in Fasciola are modified versions of mesenchymal cells. Each flame cell consists of cilia. These cells vibrate like the flickering of a flame. As they vibrate they help in waste removal from the Fasciola body. Thus, this statement is also correct.
Statement D says that earthworms are hermaphrodites still they are capable of cross-fertilization. Earthworms are indeed hermaphrodites. This means that they have both the female and male sex organs in their body. They can self fertilize and produce off-springs. But as they have both types of sex organs, they can produce female as well as male gametes. This allows them to take or give gametes and perform cross-fertilization. So, this statement is correct.
Hence, the right answer is option A.

Note: The malpighian tubule system in cockroaches is composed of slender tubes. This is a characteristic feature of many arthropods. On the other hand, the green glands in the prawn is a characteristic feature of crustaceans. These are kidney-like organs that are attached to the renal sac.