Question

What is the connecting link between phylum Annelida and Mollusca?
(a) Peripatus
(b) Neopilina
(c) Chiton
(d) Nautilus

Answer 1

Hint: This newly discovered species is a living representa­tive of the class Monoplacophora, and possesses a peculiar ­mixture of mollusks and Annelids characteristics.

Complete answer:
The connecting link between annelids and Mollusca is Neopilina. It gives birth to trochophore larvae like Annelida and also has 5 to 6 pairs of ctenidia, 6 pairs of nephridia, 8 pairs of retractor muscles, and 2 pairs of auricles like Annelida. It has a shell and mantle similar to mollusks and shows the presence of a flat muscular foot like in Mollusca.

Additional Information: -Neopilina may be a deep-sea variety and was collected from the Pacific at depths from 2500 to 5000 m. Neopilina mainly feeds on foraminifera and lives in the mud. It also takes radiolarians and diatoms as evidenced by their remains in its stomach.
-Neopilina’s body is more or less bilaterally symmetrical and possesses metameric segmentations like annelids. Neopilina galatheae is almost 3.3 cm wide, 3.7 cm long, and 1.4 cm high. The dorsal side of the body is covered by a thin shell. The shell is circu­lar in outline. The apex of the shell is slightly bent and anteriorly drawn.
-The annelids that are an outsized phylum also are referred to as the ringed or segmented worms, it includes over 22,000 extant species of ragworms, earthworms, and leeches. These species exist and have adapted to varied ecologies they are- as distinct as tidal zones and hydrothermal vents in marine environments, others in the water, as well as some others in moist terrestrial environments.
-Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. They are the most important marine phylum, comprising about 23% of all the named marine organisms. Numerous mollusks also live in freshwater and terrestrial habitats.
-Peripatus may be a genus of velvet worms within the Peripatidae family. The genus Peripatus is mainly occurring in Central America, the Caribbean, and northern South America.
- Within the Polyplacophora, chitons are marine mollusks of varying sizes. They are also sometimes referred to as sea cradles or "coat-of-mail shells".

So, the correct answer is,’Neopilina’.

Note: - Living representatives of the Class Monoplacophora were not discovered until 1952, although Paleozoic fossil monoplacophorans had been known for some time.
 -At present, 11 species are known. Most live at great depths and everyone is marine.
 -Monoplacophorans which provide them a limpet-like appearance, are small and have one, caplike shell.
-The nautilus may be a pelagic marine mollusk of the cephalopod family Nautilidae.