Match Column I with Column II and select the correct answer using answer codes given below :
Column - I: Column - II
A. Statocyst - (i) Nereis
B. Viviparous - (ii) Ctenodrilus
C. Nuchal organs - (iii) Pheretima
D. Clitellum - (iv) Arenicola

Question

Match Column I with Column II and select the correct answer using answer codes given below : 
Column - I: Column - II
A. Statocyst -  (i) Nereis
B. Viviparous - (ii) Ctenodrilus
C. Nuchal organs - (iii) Pheretima
D. Clitellum - (iv) Arenicola

Accepted Answer

The correct option is 1: A (iv), B (ii), C (i), D (iii).

The correct answer relies on correctly identifying the defining anatomical and physiological features of the four annelid genera provided.
**A. Statocyst is correctly matched with (iv) Arenicola.** A statocyst is a specialized sensory organ of equilibrium and orientation, essentially an organ of balance. It is characteristic of many marine invertebrates, including certain polychaetes like *Arenicola* (the lugworm). *Arenicola* is a burrowing marine worm that needs to maintain its orientation within the sand or mud, and its statocyst helps it perceive gravity and maintain equilibrium in its environment.
**B. Viviparous is correctly matched with (ii) Ctenodrilus.** Vivipary refers to a reproductive method where the young develop inside the parent's body and are born live, rather than hatching from eggs laid externally (oviparity). While the vast majority of Annelids are oviparous, the small aquatic oligochaete *Ctenodrilus* is a well-known exception, often cited in textbooks for its viviparous nature where multiple young can develop within the parent's segments.
**C. Nuchal organs are correctly matched with (i) Nereis.** Nuchal organs are paired, ciliated, chemoreceptive sensory pits or slits located on the prostomium (head region) of many polychaetes, such as *Nereis* (the clamworm or ragworm). These organs are crucial for detecting chemical stimuli in the surrounding water, helping the animal to locate food, assess water quality, and find mates.
**D. Clitellum is correctly matched with (iii) Pheretima.** The clitellum is a thick, saddle-like, glandular band of skin segments found only in the sexually mature members of Oligochaetes (like earthworms) and Hirudinea (leeches). Its function is highly specific: it secretes the mucus and the proteinaceous substance that forms the cocoon in which the eggs are deposited and fertilized. *Pheretima* is a common genus of earthworms where the clitellum is a prominent feature.

The incorrect option is 2: A (ii), B (iv), C (iii), D (i).
This option incorrectly pairs Statocyst with *Ctenodrilus* and Clitellum with *Nereis*. As explained, the Statocyst is a balance organ necessary for the marine life of *Arenicola*, not the small *Ctenodrilus*, which lacks this specialized organ. Furthermore, the Clitellum is a structure for cocoon formation in Oligochaetes like *Pheretima*, not a feature of the polychaete *Nereis*, which does not possess a clitellum and releases its gametes directly into the water for external fertilization.

The incorrect option is 3: A (iv), B (iii), C (i), D (ii).
This combination makes fundamental errors by matching Viviparous with *Pheretima* and Clitellum with *Ctenodrilus*. *Pheretima* (the earthworm) is a classic example of an oviparous organism, as it lays its eggs within the protective cocoon secreted by its clitellum; therefore, it is not viviparous. While *Ctenodrilus* does possess a clitellum as an oligochaete, the most biologically distinctive feature of this particular genus in reproductive terms is its viviparity, making B (viviparous) the correct and intended match.

The incorrect option is 4: A (iii), B (iv), C (i), D (ii).
This option incorrectly matches Statocyst with *Pheretima* and Viviparous with *Arenicola*. The terrestrial earthworm *Pheretima* lives entirely in the soil and does not require the sophisticated balance organ of a statocyst, which is characteristic of aquatic species like *Arenicola*. Also, *Arenicola* is oviparous, releasing its eggs externally into the water column, and is not a viviparous species.