Planispiral is a condition in which a tubicolous shell is coiled in a single horizontal plane and the diameter increases away from the axis of coiling. This term is usually used for describinggastropod shells. Manycephalopods andtubeworms can also have a planispiral shell (Allaby and Allaby, 1999).

• Allaby, A. & Allaby, M. (1999)."Planispiral".A Dictionary of Earth Sciences. Retrieved2014-01-13.

• Mollusc shells