Apex (mollusc)

Part of the shell of a mollusk

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.
Find sources: "Apex" mollusc – news · newspapers · books · scholar · JSTOR (April 2023) (Learn how and when to remove this message)

|

In anatomy, an apex (adjectival form: apical) is part of the shell of a mollusk. The apex is the pointed tip (the oldest part) of the shell of a gastropod, scaphopod, or cephalopod.

The apex is used in end-blown conches.

## Gastropods

[edit]

The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod. The apex is the first-formed, and therefore the oldest, part of the shell. [1] To be more precise, the apex would usually be where the tip of the embryonic shell or protoconch is situated, if that is still present in the adult shell (often it is lost or eroded away).

### Coiled gastropod shells

[edit]

The phrase apical whorls, or protoconch, means the whorls that constitute the embryonic shell at the apex of the shell, especially when this is clearly distinguishable from the later whorls of the shell, otherwise known as the teleoconch.

Comparison of the apical part and the whole shell of Otukaia kiheiziebisu:

*   *

### Limpet-like gastropod shells

[edit]

Where this feature is present, the space under the apex of a patellate or patelliform (limpet-like) gastropod shell is called the apical cavity.

## Scaphopods

[edit]

The apex of tusk shells is the small, open posterior end, and the opening itself is usually called the apical aperture.

## Cephalopods

[edit]

In orthocone cephalopods, the pointed end of the shell is called the apex, and shell growth is away from the apex and toward the aperture. The first chamber of the apex is sometimes called the protoconch.

## Bivalves

[edit]

The apex of a valve of a bivalve shell is the area around what is most commonly the umbo or beak. In some species the embryonic shell or prodissoconch may be present at the apex of each of the two valves.

## References

[edit]

1. ^ Dance, S. Peter (2022). Shells. United Kingdom: Dorling Kindersley Limited. p. 250\. ISBN 978-0-2415-1551-8.

* v
* t
* e

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)

* v
* t
* e

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|

* Albumen gland
* 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

This gastropod-related article is a stub. You can help Wikipedia by expanding it.

|

* v
* t
* e

*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template