Question

Which of the following mostly shows sexual dimorphism?
A. Hydra and Ascaris
B. Hydra and Oryctolagus
C. Hydra and Pheretima
D. Ascaris and Oryctolagus

Answer 1

Hint: Sexual dimorphism is a condition in which two separate sexes of a single species are observed. This means that the male and the female sexes are separate and can be determined from their external features and the outer morphology. The sex chromosomes determine the sexual nature of the species.

Complete answer: Ascaris is a member of the phylum Aschelminthes. It shows sexual dimorphism. The male and the female can be identified from their external features. Males have a posteriorly curved tail with a pineal spicule whereas, the female has a long and straight tail. Females also have gonophore.
-Oryctolagus is the European Rabbit. It is a member of mammals belonging to the phylum Chordata. It shows sexual dimorphism. The males have testes whereas the females have ovaries.
-Hydra is a member of the phylum Cnidaria. It is a unisexual organism. However, it does not show sexual dimorphism. It possesses totipotent or regenerative cells that form the sex organs. One organism forms the testes that produce the sperms. Another organism forms the ovary. The sperms swim via water and reach the ovary where fertilization occurs. Therefore, fertilization is internal.
-Pheretima is the earthworm. It belongs to the phylum Annelida. Earthworms do not show sexual dimorphism. The male and the female organs are present inside the body of a single earthworm only.
Thus, based on the above information we can conclude that Ascaris and Oryctolagus show sexual dimorphism.
Hence, the correct answer is option (D).

Note: All the organisms showing sexual dimorphism are unisexual however, all the unisexual organisms do not show sexual dimorphism. This is because in some organisms the sexes are determined by external or internal conditions. There is no clear demarcation from outside however, internally the organisms develop different sexes.