The connecting link between Annelida and Mollusca is
A. Neopilina
B. Nautilus
C. Glochidium larva
D. Veliger larva

Hint: The connecting link is an organism that has both the characteristics of Annelida and Mollusca. The species that connects these two organisms together belong to the class Monoplacophora. It is a bottom feeder, probably a deposit feeder; whilst alive, its shell is covered by a layer of mucus that might be involved in feeding or locomotion.

Complete step by step answer: The intermediary form of organisms between two groups is the connecting linkage. Such an organism will have characteristics from both classes. Some molecular results suggest that Neopilina falls within the biological group of polyplacophora and is a connecting link between Annelida and Mollusca. The annelids were a broad phylum, also classified as the ringed worms or segmented worms, of over 22,000 existing species, namely ragworms, earthworms, and leeches. After Arthropoda, Mollusca is the second-largest genus of invertebrate animals. Around 85,000 endemic species of molluscs are recognized. The amount of fossil species is approximately between 60,000 and 100,000 potential species. The largest marine phylum, representing about 23 percent of all of the marine species called, is molluscs. In marine and freshwater habitats, various molluscs also stay. Not just in size and anatomical design, but mostly in behaviour and ecosystem, they are incredibly diverse.
Hence, the correct answer is option A.

Additional information: Since annelids are tender-bodied, their fossils, mostly jaws as well as the mineralized tubes naturally produced by some of the animals, are unusual. Although some late Ediacaran fossils that depict annelids, in the early Cambrian era, the world's oldest fossil identified with strength came from around 518 million years ago. A mantle with a substantial cavity used during breathing and excretion, and also the coordination of the nervous system are by far the most fundamental aspects of the body structure of molluscs. However many have a calcareous shell. The majority of molluscs, feeding on algae or surface feeders, are herbivorous. Two feeding approaches are predominant for all those who graze. Most feed on microscopic, filamentous algae, constantly combing filaments off the seafloor using their radula as a 'rake'. Someone else feeds on macroscopic 'plants' like kelp, with all its radula rasping the ground of the plant.

Note: A lone dome-shaped shell resembling limpet shells is present in Neopilina. These are remnants of a form of organism previously extinct. For both plants and animals, living fossils arise. Neopilina’s innovation and incidence at great depths contributed to confirm a theory held by certain scientists that there is still a large percentage of 'ancient life' in the ocean depths.