Question

The mollusk which is considered to be a living fossil and also shows characters of annelids like nephritis and internal segmentation is
(a) Pinctada Vulgaris
(b) Nautilus
(c) Neopilina galatheae
(d) None of the above

Answer 1

Hint: It is the most primitive mollusk. It has internal metameric segmentation and 5 pairs of nephridia.

Complete answer: The mollusk is considered to be a living fossil and also shows characters of annelids like nephridia and internal segmentation is Neopilina galantheca.
Most of them are marine. They have huge numbers of in-shore, that is, in shallow water. With about 85,000 living species, they are the largest marine phylum, which is about 23% of all named marine organisms. They also occur in freshwater as well as on land.

        Dorsal view Ventral view  

                      Diagram showing external features of Neopilina  

Additional Information:
1. Mollusks are extremely varied: they have great diversity. That may be why there is no word in English for the phylum as a whole. "In an evolutionary sense, mollusks are plastic material".
2. Most mollusks bear shells, but some groups do not bear shells such as octopods, slugs, and the gastropods known as sea slugs.

So the correct answer is ‘ Neopilina galatheae ’

Note:
1. The three most common features that define modern mollusks are the presence of a mantle with a cavity used for breathing and excretion, the presence of a radula, and the structure of the nervous system.
2. Mollusks have much more variety existing on earth than their ancient rivals, the brachiopods.