Planispiral

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).

References

• Allaby, A. & Allaby, M. (1999). "Planispiral". A Dictionary of Earth Sciences. Retrieved 2014-01-13.

External links

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Cephalopod anatomy

Shell

Types	External Ammonoid shell Argonautid eggcase Nautiloid shell Orthocone Internal Belemnoid guard Cirrate shell Cuttlebone Gladius (pen) Spirula shell Stylet
Features	External Aperture Apex Callus Lirae Periostracum Sculpture Spire Sutures Umbilicus Internal Body chamber Camerae Nacre Phragmocone Septa Siphuncle Whorls

Mantle &
funnel

External anatomy	Dermal structures Fins (wings) Flotation devices ("secondary fins") Funnel–mantle locking apparatus Tail
Internal anatomy	Branchial hearts Ctenidia (gills) Hepatopancreas (digestive gland) Ink sac and ink Needham's sac Nephridia ("kidneys") Nidamental glands Osphradium Pericardial glands

Head &
limbs

Brachial crown	Arms Hectocotylus Tentacles Carpus Dactylus Manus Suckers and hooks
Buccal region	Aptychus Beak Odontophore Radula Spadix and antispadix
Occipital region	Nuchal crest (occipital crest) Nuchal folds (occipital folds) Occipital membrane Olfactory organ Nuchal organ
Other parts	Eyes Statocysts

General

• Chromatophores
• Photophores
• Nervous system
  • Squid giant axon
  • Squid giant synapse

Developmental stages: Spawn → Paralarva (Doratopsis stage) → Juvenile → Subadult → Adult • Egg fossils • Protoconch (embryonic shell)