Mollusca MCQ: Introduction and Explanation

Ans. (c) Cephalopoda.

Explanation: Octopus is a part of the phylum Mollusca. Mollusks are classified into 7 classes and Cephalopoda is one of them. Animals belonging to class Cephalopoda have soft-bodied animals with multiple arms attached to their heads and a mantle covering their visceral organs. The features are all present in an Octopus, therefore Octopus is a cephalopod.

Ans. (c) Mytilus belongs to class Pelecypoda of phylum Mollusca

Explanation: Mytilus is a genus for saltwater mussels belonging to class Pelecypoda of Molluscs. They have organisms with two shells therefore, they are called Bivalves. These valves are equal in size and are hinged at the back. Between these shells is the soft-bodied invertebrate with a muscular foot.

Ans. (b) Unio has a three-chambered heart.

Explanation: Unio is a genus for mussels, belonging to the phylum Mollusca. They have three-chambered hearts with 2 atriums and 1 ventricle. Their heart pumps blood from the gills. Mollusks have an open circulatory system with blood flow contained in blood vessels.

Ans. (b) Cephalopoda

Explanation: Class Cephalopoda of Phylum Mollusca has animals such as squid, cuttlefish, and octopuses. These are the most neurologically advanced and the most intelligent of all invertebrates. The word Cephalopoda means "head foot" and they have the most complex brain. They form an important example of advanced cognitive evolution amongst animals in general.

Ans. (d) Sea feather

Explanation: The sea pen or sea feather however is not a mollusk it belongs to the phylum Coelenterata. Aplysia or sea hare is a genus of slugs. They are gastropods and have parapodia which they use for swimming, respiration, and locomotion. Doris is another genus of sea slugs; they are marine molluscs and are commonly known as sea lemons. They feed on encrusting organisms. Chiton or sea cradles are another groups of marine molluscs. Their class is Polyplacophora. These animals have a dorsal shell which is composed of many shell plates. These are found in different parts of the world and both warm as well as cold water.

Ans. (a) Crustacea

Explanation: The phylum Mollusca of the animal kingdom is divided into 7 classes namely- Aplacophora, Monoplacophora, Polyplacophora, Bivalvia or pelecypoda, Gastropoda, Cephalopoda, and Scaphopoda. Crustacea is not a class of phylum Mollusca but Arthropoda.

Ans. (d) Octopus.

Explanation: Octopus has eight muscular arms or tentacles. The common octopus is sometimes called a Devil Fish because of this appearance. In ancient times, this appearance was considered evil by fishermen and sailors, therefore the word Devil. Some octopuses live in very shallow waters but most of them are found close to the ocean bed.

Ans. (b) Nacre.

Explanation: Nacre or the nacreous layer is also known as the mother of pearl layer. It contains aragonite crystals and organic-inorganic composite material produced by some mollusks as a layer for the inner shell; it is called the pearl mother layer because it contains the material of which pearls are made.

Ans. (c) Pelecypoda

Explanation: Pearl, a precious gem used for making jewelry, is the product of the secretion of a pearl oyster or a mussel. The pearl is produced by the bivalves of Mollusca. These bivalves are marine animals and produce superior-quality pearls. Some freshwater mussels also produce pearls but it is of inferior quality and is not of much use. Mussels belong to class pelecypoda of phylum Mollusca.

Ans. (a) Absence of head

Explanation: Bivalvia is a class of Mollusca, also known as Pelecypoda. Organisms of this class are characterized by having a two-valve shell. The shell has right and left halves and is hinged at the back. What makes Bivalves distinctive is that they lack ahead. There is no proper cranium. The organisms don’t have radula and jaws as well.

Ans. (c) Neopilina galatheae

Explanation: Molluscs are not a group of segmented organisms but Neopilina is an exception. It is one of the most primitive molluscs. It has characteristics of annelids like earthworms such as internal metameric segmentation, 5 pairs of nephridia, hearts, gills, and more. This mollusc is truly a living-fossils that has become the connecting link between annelids and molluscs.

Ans. (a) Triploblastic and coelomate

Explanation: It is the characteristic feature of Molluscs to be triploblastic and coelomate. They also have bilateral symmetry and their soft body is covered with a hard calcareous shell. The soft-bodied molluscs have a mantle over their visceral organs. They also have gills present in the mantle cavity for respiration.

Ans. (d) These are mostly aquatic animals with an unsegmented soft bodies and a shell mostly.

Explanation: The phylum Mollusca is the largest marine phylum containing majorly aquatic animals, some live in freshwater but the majority are found in marine water. These animals are unsegmented and soft. Some of these animals have a hard shell, they are triploblastic and bilaterally symmetrical. Examples of these organisms are Octopus, Slugs, Squids, Mussels, Chitonida., etc.

Ans. (a) Architeuthis.

Explanation: Architeuthis is a giant squid living deep in the ocean. These giant squids can grow up to the size of 13 m is about 43 ft for females and 10 m that is 33 ft for males. They weigh nearly a ton. Measurements are taken from the posterior fins to the tip of the long tentacles. It is the largest invertebrate.

Ans. (b) Haemocyanin in the blood plasma

Explanation: Haemocyanin is the respiratory pigment in the molluscs which dissolves in plasma. It is found as a pigment in the blood of molluscs, arthropods, and crustaceans. This pigment is blue due to the presence of copper which binds to the oxygen molecules. It helps in the exchange of gases or respiration as well as exertion.