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 describing

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

shells. Many

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

s and

tubeworm A tubeworm is any worm-like sessile invertebrate that anchors its tail to an underwater surface and secretes around its body a mineral tube, into which it can withdraw its entire body. Tubeworms are found among the following taxa: * Annelida, the ...

s can also have a planispiral shell (Allaby and Allaby, 1999).

References

External links

{{Gastropod anatomy Mollusc shells