Explain the classification of phylum mollusca of non chordates?

The phylum mollusca are divided into different classes which are known as monoplacophora, amphineura, scaphopoda, gastropoda, pelecypoda and cephalopoda. The monoplacophora are known as single plate bearing animals. Their shell is spoon shape with tentacles on the head. They are the connecting link between phylum mollusca and annelid. As they have internal segmentation and consists of nephridia which are the prominent features of annelid. They have mantle, shell and foot which are the prominent features of mollusca. They are mainly marine. The amphineura are also known as the organism with both nerves. They are mainly marine and have mantle, shell and foot which may or may not be present. They do not have eyes and tentacles. They have a nerve ring around the mouth with 4 nerve cords which are interconnected. The nerve ring are non ganglionated. The scaphopoda are also known as boat foot organisms. They do not have eyes and tentacles and are mainly marine. They can also occur in the burrows. Their foot is conical which helps in the digging. They have a tubular shell which opens at both the ends. The gastropoda are also known as the belly foot organisms. They do have eyes and tentacles and have terrestrial, marine and fresh water forms. Their foot is flat and muscular and the shell is of single piece. The early form of this organism is symmetrical but later on it becomes asymmetrical as it becomes twisted. It has the largest number of mollusca. The pelecypoda are also known as the hatchet foot organisms. Their foot is hatchet in the shape and is used for digging. They do not have eyes and tentacles and can be marine or fresh water. Their shell is made up of two parts. The cephalopoda are also known as head foot organism. In this type the head and foot are combined and form a head foot. It bears eyes and have multiple tentacles. Their eyes form image and are the top most invertebrates in relation to their behavior. They are mainly marine and act as active predators. They are the largest invertebrates and are also known as the giant squids. They are nearly 20m long. There shell can be external, internal or absent.
There is a living fossil named neopilina which shows the metameric segmentation. It is not a characteristic feature of mollusca. It has 16 segmented muscles and 12 gills with 10 nephridia. The mollusca are derived from annelid and it can be suggested by this evidence. First there is a formation of trochophore larva which is quite similar to annelid. Secondly, there is a metameric segmentation. So, neopilina act as a link between annelid and mollusca.
Chiton is also known as the coat of mail shell. It is marine and occurs in the tide. It is active during night and is herbivorous. It is attached to the rock and can be detached. Their body is oval in shape and has a covering of shell. The shell has a row of 8 plates with a flat and elongated foot. The dentalium is also known as elephant’s tusk shell. It is mainly marine and occurs in the sand. They respire by mantle. The shell is like a tube with both open ends. Their foot is pointed and helps in digging. There are filamentous tentacles present in the tusk shell known as captacula. The unio is also known as fresh water mussel. It occurs in rivers and ponds. They are omnivorous and eat small organisms. Its larva lives like a parasite. Their shell is divided into two halves. There is a presence of hinge ligament which joins the two halves of shell. There is a swelling in the valve known as umbo. There are lines of growth which tell about the age of individual. They have two siphons which are known as inhalant and exhalent siphons. The inhalant siphon is the siphon through which water enters and there is an exhalent siphon through which water is passed out. They act as a food for man and animals. They also act as scavenger and keep the water clean. The shells are an excellent source of lime and help in the making of buttons.
The pearl is a small shell which are secreted by a bivalve and oyster when there occurs an injury or irritation. It is made up of calcareous material which is covered by many layers of nacreous material. The pearl oyster is the most common and the best quality pearl. It is sedentary and is reared artificially. Japan is the most important source of pearls in world. There are fine silica material between mantle and shell. The mantle secretes nacre which forms the pearl. It was introduced by Mikimoto.
The pila are also known as apple snail. It occurs in fresh water and is mainly herbivorous. It feeds on the plants present in the water so it leads an amphibious life. The mode of respiration is by gills in water and by lungs on the land. So, it can live on land and water. The shell is a single piece which is protective in function. The coils of the shells are known as whorls. There is a structure known as operculum which is oval in shape and encloses the mouth. The head has tentacles, eyes and mouth. There is a muscular foot which is flat. Limax is also known as grey slug. It lives on land and on moist soils. It is active during night and is herbivorous. Their body is differentiated into head, foot and visceral hump. The head has a mouth, lips, genital pores and tentacles. The tentacles have a black eye. Their shell is internal and is hermaphrodite. Their foot is developed and has pulmonary aperture. It is a plant pest which damages leaves, shoots etc. The sepia is also known as cuttle fish. They are mainly marine and occur in the shallow water which is warm. They are good in swimming and are carnivorous. Their body is differentiated into head, neck and trunk. The head has eyes and 10 arms. Each arm has has 4 rows of suckers. The 4th pair of arms is known as tentacles which have suckers. Their neck is small and the trunk has fins on their sides which help in the swimming. A structure known as funnel is present below the head. Their shell is internal. They have an ink sac which contains ink like fluid. They form a smoke cloud when they are attacked. They are edible and the ink is used by artists. The shell is used as a source of calcium. Loligo are also known as squid. They are mainly marine and occur in the shallow water which is warm. They are good in swimming and are carnivorous. They have an ink sac which contains ink like fluid which forms a smoke cloud when they are attacked. Their shell is internal. Their body resembles that of sepia. It is edible. This is the largest invertebrate. The octopus is also known as devil fish. It occurs in the bottom of sea and is nocturnal. It feeds on other animals and kills its prey by the saliva which is poisonous. Their body is divided into head and trunk. The head consists of eyes, funnel, arms and suckers. The arms are united and form a web. They have no shell. The arm is spoon shape which transfers the sperms to female and is known as hectocotylized.