Other Classes
Class Polyplacophora
This class consists of chitons. They have a radula, a reduced head, a flat foot, a shell that is segmented into eight parts, a mantle that goes past the edge of the shell and covers the whole foot, a mantle cavity that is limited to the space between the mantle and the foot, a foot that allows the organism to stick to surfaces, a series of gills that are on both sides of the foot, and a ladderlike nervous system with anteroposterior nerve cords and transverse nerves. They eat mostly algae and use chemoreceptors to find their food. They trap their food in mucus and then its is carried by cilia into the esophagus, which is surrounded by a nerve ring. In the stomach their food is digested and absorbed extracellularly. When chitons are removed from the surface that they are sticking on they will curl up into a ball. Polyplacophora are monoecious that fertilize externally with free-swimming trochophores that develop without becoming a veliger larvae.
Class Scaphopoda
This class consists of tusk shells or tooth shells. They have a radula, tentacles, an elongated shell that is open at both sides, a head and foot that is located at the bigger shell opening, and visceral mass and mantle that goes the whole length of the shell. They spend most of their time buried under the sand with the smaller opening pointing up into the water. Water enters and exits through this opening. These molluscs don't have gills, instead gases are exchanged using the folds of the mantle. Scaphopoda are monoecious and they produce trochophore and veliger larvae.
Class Monoplacophora
This class is extinct except for only one known species that is still living, which is Neopilina. They have a pair of gills, a shell thats is curved and unsegmented, a foot that is flat and wide, and foot-retractor muscles which allow the organism to move their foot. Monoplacophora are dioecious but the embryology of the organism is unknown.
Class Aplacophora
This class is separated into two subgroups: Neomeniomorpha and Chaetodermomorpha. Neomeniomorpha, known as solenogasters, have a ladderlike nervous system and a body similar to flatworms, but lack a shall and most lack a radula and nephridia. Chaetodermomorpha have scalelike spicules but lack a shell, a foot, a crystalline style, statocysts, and nephridia. There are approximately 120 species of Alpacophora.