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Placipodia ("plated foot") is a class of kinespetrod having a dorsal shell made up of between five and nine (always an odd number) 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 100,000 species.
The class is mostly terrestrial, but there are aquatic species. Placipods typically have a well-defined head with two to six sensory tentacles, and a ventral foot. The eyes that may be present at the tip of the tentacles range from simple ocelli that cannot project an image to more complex pit and even lens eyes. The majority of the body beyond the girdle is not visible from the dorsal side. Between the body and the girdle, there is a mantle cavity. Almost all aquatic species breathe with gills, but some freshwater species, and all terrestrial species, have a pallial lung.