Question

The nuchal organ is a ciliated pit or groove, present at the posterior end of the prostomium in a group of organisms. It is used in light detection and food detection. Organisms of which phylum possess this organ?
(a)Annelida
(b)Arthropoda
(c)Aschelminthes
(d)Platyhelminthes

Answer 1

Hint: The nuchal organ is possessed by the organisms of the phylum which has the characteristic feature of metamerism i.e. their body is segmented into little rings or “metameres”. The nuchal organ is also seen in some cephalopods.

Complete answer:
The nuchal organ is a groove-like structure present near the posterior (backside) end of the prostomium of annelids. The main functions of this organ include the detection of light and food. It is also utilized for mating. Hence, they are known as epidermal sensory organs.

Additional Information: Let us learn more about the phyla mentioned in the options.
Annelida: Annelids are triploblastic, coelomate, and metamerically segmented with an organ-system level of body organization. They have nephridia for excretion and osmoregulation. Examples include earthworm and leech
Arthropoda: Arthropods belong to the largest phylum of the animal kingdom. Their body is divided into a head, thorax, and abdomen. The reason for their success in evolution is credited to their chitinous exoskeleton. Examples: Apis, Bombyx, Anopheles
Aschelminthes: They are commonly known as roundworms because their body is circular in a cross-section They are pseudocoelomate, triploblastic animals with muscular pharynx Examples- Ascaris, Wuchereria.
Platyhelminthes: They are commonly known as flatworms because they have a dorso-ventrally flattened body. They are mostly found as endoparasites. Examples- Planaria, Taenia
So, the correct option is ‘Annelida’.

Note: -Prostomium is the first segment of an annelid which is cephalized i.e. head-like structure.
-Malpighian tubules are the excretory structures present in arthropods.
-The roundworm Wuchereria causes elephantiasis in human beings.