Callus (mollusc)

The shell of the sea snail Neverita josephinia has an umbilical callus which almost completely fills the umbilicus, leaving only a groove open.

A callus is an anatomical feature that exists in some mollusk shells, a thickened area of shell material that can partly or completely cover the umbilicus, or can be located as a coating on the body whorl near the aperture of the shell (i.e. a parietal callus or columellar callus).

A callus exists in the shells of various species of gastropods (snails) and also in the shells of several species of Nautilus, a cephalopod.

The shell of the sea snail Semicassis pyrum, has a large aperture and a pronounced parietal callus

A callum is an anatomical feature of some mature bivalve shells of species in the family Pholadidae, the piddocks. The callum is an area of shell material that fills the gap between the two valves.^[1]

References

↑ Definitions of terms for parts of gastropod shell

Look up callus in Wiktionary, the free dictionary.

Bivalve anatomy

Shell	Callus Hinge line Hinge teeth Ligament Lira Lunule Nacre Pallial line Pallial sinus Periostracum Prodissoconch Resilifer Resilium Sculpture Umbo Valve Beak Annuli

Other hard parts	Byssus Pearl Sea silk

Soft parts	Adductor muscles Ctenidium Gastric shield Mantle Nephridium Siphon

Other	Abductin Glochidium Pseudofeces Trochophore Veliger

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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