Question

Which of the following belongs to the class Amphineura?
A. Chiton
B. Nautilus
C. Dentalium
D. Pinctada

Answer 1

Hint: Based on symmetry, body, mantle, gills, food, nervous system, muscles, and radula, mollusks are divided into 6 groups. Amphineura is one of these 6 classes. (Gr. amphi = both, nerve = neuron).

Complete answer: Amphineura is generally referred to as sea cradles or Chitons, and many plate bearers have a literal meaning. They are found in marine habitats. They can be found from shallow water to the deep ocean. The cells of Amphineura are composed of eight overlapping dorsal plates at the front and back edges. On the outer rim, these plates are linked together and pass internally to the girdle. The thick portion of the mantle is the girdle. Girdles may have scales, spines or bristles; their plates are flexible, assisting them with locomotion. Shells also provide the animals with protection. The animal shells are arranged in such a way that when they are dislodged on an uneven surface, it has Chitons to roll into a safe disc.
-The only cephalopod that has an outer shell is the Nautilus genus. It is the oldest cephalopod actually belonging to the Nautiloidea subclass. Their shells mimic snail shells. Their shells are coiled spirally and are found to be multi-chambered.
-Under the genus Dentalium, the elephant tusk is described. It is a scaphopod mollusk genus. At the top, they are greenish, fading to white. With the assistance of a boat-like foot, such a tusk shell is used for burrowing the sand. The head, the gills, and the eyes are missing. The radula is simple and the nephridia are responsible for excretion. These mollusks live on the sediment of the seafloor, feeding on detritus of microscopic organisms, etc.
-Pinctada is a genus of marine bivalve mollusks that are saltwater clams. They belong to the Pteriida tribe. Such oysters have a dense inner shell layer composed of a nacre that is activated and the tissue secretes a fluid collected to form the pearl. So, they are known as pearl oysters.
So, the correct answer is option A, i.e., Chiton.

Note: There are tentacles or cephalic eyes for Amphineura. They have an anterior mouth with a radula. They feed on algae. Radula helps to extract the algae from the hard surfaces. Tiny crustaceans may also feed on certain animals.