Final Answer:
The intromittent organ of male cephalopods is:
d. hectocotylus
Step-by-step explanation:
The hectocotylus is a specialized reproductive arm found in male cephalopods, such as squids and octopuses. It serves as the intromittent organ, which is essential for transferring sperm to the female during mating. The hectocotylus undergoes modifications in structure and function, adapting for the specific reproductive needs of different cephalopod species.
During copulation, the male cephalopod uses the hectocotylus to transfer packets of sperm, called spermatophores, directly into the female's mantle cavity. This unique reproductive adaptation enhances the efficiency of fertilization and allows for a more direct and controlled transfer of genetic material. The hectocotylus is a remarkable example of evolutionary specialization, showcasing the diverse and fascinating adaptations that have evolved within the cephalopod class for successful reproduction.
While the other options listed—radula, tentacle, and siphon—are significant anatomical features of cephalopods, none of them function as the intromittent organ during reproduction. The radula is a feeding structure, the tentacle is used for capturing prey, and the siphon is involved in jet propulsion for locomotion. The hectocotylus, however, stands out as a distinct and specialized reproductive structure unique to male cephalopods, playing a crucial role in the continuation of their species through efficient sperm transfer during mating.