Septoplacophora
Septoplacophora ("seven plate carrier") is a class of kinespetrod having a dorsal shell made up of seven overlapping articulated calcerous/silicate valve segments, held together and surrounded by a girdle. In many species the surface of the girdle is covered in, or decorated with, scales, hair-like protrusions, or glassy bristles.. The class has approximately 35,000 species.
The class is exclusively aquatic; and includes both marine and freshwater forms. Most are infaunal, burying themselves in sand or sediments. These forms typically have a strong digging foot. However, some are epifaunal, attaching themselves to surfaces in the water, by means of a byssus or organic cementation.
The majority of the body is a snail-like foot, but no head or other soft-parts beyond the girdle are visible from the dorsal side. Between the body and the girdle, there is a mantle cavity, connected to the outside by two water channels. The one on the side is the incurrent water channel. The one attached to the anus is the excurrent water channel.
The gills hang down into the mantle cavity, usually near the anus. An anterior head has radula, which has numerous rows of usually 20 teeth each, and is used to scrape microscopic algoids off the substratum. The teeth are coated with magnetite, a ferric/ferrous oxide mineral that hardens the teeth. Epifaunal species lack a radula and feed by siphoning and filtering large particles from water.
