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 shells. Many cephalopods and tubeworms can also have a planispiral shell (Allaby and Allaby, 1999).
Cephalopod anatomy
| ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Shell |
| |||||||||||||
Mantle & funnel |
| |||||||||||||
Head & limbs |
| |||||||||||||
General |
| |||||||||||||
Developmental stages: Spawn → Paralarva (Doratopsis stage) → Juvenile → Subadult → Adult • Egg fossils • Protoconch (embryonic shell) |