Planispiral

View of the spire side of the planispiral shell of the freshwater snail Anisus septemgyratus. This shell has seven and a half whorls

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

Cephalopod anatomy

Shell

Shell types	External shells: Ammonoid shell Argonautid eggcase Nautiloid shell Orthocone Internal shells: Belemnoid guard Cirrate shell Cuttlebone Gladius (pen) Spirula shell Stylet

External features	Aperture Apex Callus Lirae Periostracum Sculpture Spire Sutures Umbilicus

Internal features	Body chamber Camerae Nacre Phragmocone Septa Siphuncle Whorls

Mantle

External anatomy	Funnel Dermal structures Fins (wings) Mantle locking-apparatus

Internal anatomy	Branchial hearts Ctenidia (gills) Hepatopancreas (digestive gland) Ink sac and ink Needham's sac Nephridia ("kidneys") Nidamental glands Osphradium Pericardial glands

Head and limbs

Brachial crown	Arms Hectocotylus Tentacles

Buccal region	Aptychus Beak Odontophore Radula Spadix and antispadix

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)

Gastropod anatomy

Shell	Aperture Apex Body whorl Callus Columella Lip Lira Nacre Periostracum Peristome Planispiral Plait Protoconch Sculpture Selenizone Siphonal canal Siphonal notch Spire Stromboid notch Suture Umbilicus Valve Varix Whorl

Other hard parts	Clausilium Love dart Operculum Pearl Radula

External soft parts	Caryophyllidia Caudal mucous pit Cerata Cnidosac Mantle Mentum Notum Parapodium Pneumostome Rhinophore Semper's organ Siphon Suprapedal gland

Internal soft parts	Circulatory system of gastropods Crop Ctenidium Digestive system of gastropods Diverticula Excretory system of gastropods Gastric shield Hancock's organ Hepatopancreas Hypobranchial gland Nephridium Nervous system of gastropods Nidamental gland Odontophore Oesophageal pouch Osphradium Reproductive system of gastropods Respiratory system of gastropods Sensory organs of gastropods

Other	Epiphragm Pseudofeces Torsion Circumesophageal nerve ring Trochophore Tyrian purple Veliger

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