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Parts of a Gastropod Shell

Shell identification guides become easier to use with some background on the morphological features present in different shell types. Check out this background information on parts of a Gastropod shell to help you identify shells to that species level identification!

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Parts of a Gastropod Shell

There are key areas of a gastropod shell that can be useful in identifying and differentiating species. Some of these characteristics include:

  • Protoconch

  • Shell whorl

  • Spire

  • Aperture

  • Outer lip

  • Siphonal Canal

  • Shell Sculpture

  • Chirality

What is a shell whorl?

 A shell whorl is one 360 degree rotation of this shell spiral. These can often be seen as "layers" down the spire of the shell. Each shell has a single Body Whorl. This is the largest section of the shell where the gastropods body resided at the latest stage of growth. The smaller shell whorls make up the Spire of the shell. 

What is a shell whorl?
Gastropod shell aperature and operculum

What is a shell aperture?

The aperture is the primary opening in the shell that the mollusk body, foot, and head enter and exit in order for it to interact with the environment. Living gastropods have an operculum, a hard calcified "door" that they can use to plug up the aperture. The operculum allows them to seal of from the outside protecting them from predators or other dangerous environmental conditions.

Shell Sculpture

The texture on the outside of a shell is called the shell sculpture. Shell sculpture is typically oriented in one of two ways, parallel or perpendicular to the axis of coiling (shown in red). Sculpture arranged parallel to the axis of coiling is called axial sculpture while sculpture arranged perpendicular to this axis is spiral sculpture.

Shell sculpture spiral vs axial
 
Shell Chirality Left vs Right

What is chirality?

Most gastropods have spiral shells. This spiral shape allows them to extend the shell from the aperture to make a continuously larger compartment for their bodies as they grow. Chirality refers to the direction in which the shell spirals. 

To determine a shells chirality hold it with the aperture facing you and the spiral of the shell pointing up. If the aperture is on the right side of the shell it is Dextral (right-handed) and if its on the left the shells is Sinistral (left-handed).