Connecting link between annelida andmollusca : a)Cuttle fish b)Octopusc)Neopilinad)NautilusCorrect answer is option 'C'. Can you explain this answer?

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The connecting link between annelida and mollusca is Neopilina galathea

Answer

Connecting link between Annelida and Mollusca: Neopilina

Neopilina is considered the connecting link between the phyla Annelida (segmented worms) and Mollusca (mollusks) due to its transitional characteristics that exhibit features from both phyla. It is an ancient marine animal that belongs to the small class Monoplacophora.

1. Annelida:
Annelida is a phylum comprising segmented worms. They possess a segmented body with distinct repeated units called metameres. Annelids have a well-developed coelom, which is a fluid-filled body cavity. They also have a closed circulatory system, a ventral nerve cord, and a metanephridia system for excretion.

2. Mollusca:
Mollusca is a phylum that includes diverse organisms such as snails, slugs, clams, squids, and octopuses. Mollusks have a soft body protected by a hard shell in some species. They possess a muscular foot for locomotion, a mantle that secretes the shell, and a radula for feeding. Mollusks also have an open circulatory system and a well-developed nervous system.

Features of Neopilina:
Neopilina is a primitive mollusk-like organism that displays characteristics of both Annelida and Mollusca. It provides crucial evidence of the evolutionary relationship between these two phyla.

1. Segmented Body: Neopilina exhibits a partially segmented body, similar to annelids. However, the segmentation is not as pronounced as in typical annelids.

2. Metamerism: Like annelids, Neopilina shows metamerism, with the presence of repeated body segments.

3. Shell: Neopilina possesses a protective, calcareous shell, which is a characteristic feature of mollusks. The shell is similar in structure to that of some gastropods.

4. Mantle: Neopilina has a mantle, a fold of the body wall that secretes the shell, resembling the mantle found in mollusks.

5. Radula: Although not as developed as in other mollusks, Neopilina possesses a radula, a feeding structure present in mollusks, which consists of rows of teeth used for scraping food.

6. Primitive Nervous System: Neopilina has a relatively simple nervous system, consisting of a nerve ring and paired ventral nerve cords, resembling the nervous system of annelids.

7. Primitive Excretory System: Neopilina exhibits a primitive excretory system with protonephridia, which are similar to the excretory organs found in some annelids.

Therefore, Neopilina serves as a crucial linking species between Annelida and Mollusca, displaying characteristics from both phyla and providing evidence of their evolutionary relationship. Its intermediate features suggest a common ancestry and evolutionary divergence that led to the development of the distinct characteristics observed in modern annelids and mollusks.

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