Identifying terrestrial gastropods

Measuring terrestrial gastropods

Measurement can be a useful characterCharacter:
1). A distinctive trait, quality or attribute used for recognizing, describing, or differentiating taxa; 2). The term used to denote such descriptive traits that possess states and are located within the Lucid version 2 (and later) interactive matrix panel. (compare feature)
in the identification of a terrestrial gastropodGastropod:
A single-shelled mollusc.
. In snails, the length is taken from the apexApex:
The tip of the spire of a shell.
of the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
to the baseBase:
This is the lower or underside of the shell; opposite of apical.
of the apertureAperture:
The major opening of a shell that the body of the animal may be retracted.
(mouth). The widthWidth:
The width of the shell is the maximum distance across the shell (including the aperture).
should be taken at the widest part of the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
when the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
is oriented so that apertureAperture:
The major opening of a shell that the body of the animal may be retracted.
faces the observer; the widthWidth:
The width of the shell is the maximum distance across the shell (including the aperture).
is measured from the side of the body whorlBody whorl:
The large, final coil (most recently formed) of a mollusc shell that contains the body of the snail, i.e. from the aperture to approximately one whorl back.
to the outermost side of the apertureAperture:
The major opening of a shell that the body of the animal may be retracted.
(mouth). Terrestrial slugs are measured from the headHead:
The area of a mollusc's body that has the tentacles, eyes and mouth.
, excluding the tentaclesTentacles:
Sensory projections on the head end of a mollusc. There are generally two pairs; upper (posterior) and smaller, lower (anterior). The upper pair bears the eyes. In many snails the eyes are located at the tips of this structure; however, in Basommatophoran snail species, the eyes are located at the base of the tentacles.
to the tip of the tail. It is important that the animal is fully extended to in order to obtain an accurate measurement.

Umbilicus

The umbilicusUmbilicus:
A navel-like indentation or depression in the center of the shell. It may be described as open (inside of columella visible), partially closed (partly covered by base of aperture) or completely closed (not visible). The width of the umbilicus is a measure of its greatest diameter.
may be used as a diagnostic characterCharacter:
1). A distinctive trait, quality or attribute used for recognizing, describing, or differentiating taxa; 2). The term used to denote such descriptive traits that possess states and are located within the Lucid version 2 (and later) interactive matrix panel. (compare feature)
when classifying snails. The umbilicusUmbilicus:
A navel-like indentation or depression in the center of the shell. It may be described as open (inside of columella visible), partially closed (partly covered by base of aperture) or completely closed (not visible). The width of the umbilicus is a measure of its greatest diameter.
may be open or closed. The widthWidth:
The width of the shell is the maximum distance across the shell (including the aperture).
of the open umbilicusUmbilicus:
A navel-like indentation or depression in the center of the shell. It may be described as open (inside of columella visible), partially closed (partly covered by base of aperture) or completely closed (not visible). The width of the umbilicus is a measure of its greatest diameter.
is taken at the widest part of the inner surfaces of the body whorlBody whorl:
The large, final coil (most recently formed) of a mollusc shell that contains the body of the snail, i.e. from the aperture to approximately one whorl back.
.

Counting whorls

There are several ways to count the number of whorlsWhorls:
Pleural of whorl. A whorl is a complete spiral turn/growth of the shell of a mollusc. The whorls are counted from the apex outwards.
on the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
of a snail. The most commonly used method described by Pilsbry (1939) will be discussed here. Before counting the whorlsWhorls:
Pleural of whorl. A whorl is a complete spiral turn/growth of the shell of a mollusc. The whorls are counted from the apex outwards.
, an imaginary line should be drawn across the shellShell:
A hard, inflexible, calcareous or chitinous structure that vary in size and may either completely encasing the animal, covering some part of it or be internal.
as demonstrated below. The whorlsWhorls:
Pleural of whorl. A whorl is a complete spiral turn/growth of the shell of a mollusc. The whorls are counted from the apex outwards.
are then counted following the direction of the coils. A complete turn indicates a whorlWhorl:
A complete spiral turn/growth of the shell of a mollusc. The whorls are counted from the apex outwards.
(i.e., every time the line is intersected when following the whorlsWhorls:
Pleural of whorl. A whorl is a complete spiral turn/growth of the shell of a mollusc. The whorls are counted from the apex outwards.
). The body whorlBody whorl:
The large, final coil (most recently formed) of a mollusc shell that contains the body of the snail, i.e. from the aperture to approximately one whorl back.
may not be complete, meaning that it may end in quarters or thirds.