*COMMENT ~ Orders: Character notes. 
 
*CHARACTER NOTES 
#1. \i{}Univalve\i0{}: a shell consisting of one piece.
\par{}\i{}Bivalve\i0{}: a shell composed of two plates, hinged together.
#8. \i{}Mantle\i0{} of molluscs: the fleshy or membranous covering of
that part of the body (usually anterior) which usually secretes the
shell, and which encloses the mantle cavity. The latter functions as a
lung, and connects with the exterior via a \i{}respiratory pore\i0{}
(pneumopore) in the mantle. \par{}Illustrations of the principal
structures referred to in routine descriptions of land and freshwater
molluscs can be accessed via the Terminology toolbar button. 
#9. \i{}Mantle\i0{} of molluscs: the fleshy or membranous covering of
that part of the body (usually anterior) which usually secretes the
shell, and which encloses the mantle cavity. The latter functions as a
lung, and connects with the exterior via a \i{}respiratory pore\i0{}
(pneumopore) in the mantle. \par{}Illustrations of the principal
structures referred to in routine descriptions of land and freshwater
molluscs can be accessed via the Terminology toolbar button. 
#16. \i{}Mantle\i0{} of molluscs: the fleshy or membranous covering of
that part of the body (usually anterior) which usually secretes the
shell, and which encloses the mantle cavity. The latter functions as a
lung, and connects with the exterior via a \i{}respiratory pore\i0{}
(pneumopore) in the mantle. \par{}Illustrations of the principal
structures referred to in routine descriptions of land and freshwater
molluscs can be accessed via the Terminology toolbar button. 
#19. \i{}Mantle\i0{} of molluscs: the fleshy or membranous covering of
that part of the body (usually anterior) which usually secretes the
shell, and which encloses the mantle cavity. The latter functions as a
lung, and connects with the exterior via a \i{}respiratory pore\i0{}
(pneumopore) in the mantle. \par{}Illustrations of the principal
structures referred to in routine descriptions of land and freshwater
molluscs can be accessed via the Terminology toolbar button. 
#20. \i{}Operculum\i0{}: a horny or calcareous plate, borne on the foot
of Gastropoda-Prosobranchia, which seals the mouth of the shell when the
animal retracts into it. It is not to be confused with the mucous plug
(epiphragm) with which many land snails seal the shell when
over-wintering or in order to withstand dry conditions.
\par{}\i{}Clausilium\i0{}: a flexible, spoon-shaped plate, attached to
the columella, which blocks the entrance when the animal withdraws.
Characteristic of Clausiliidae. \par{}Illustrations of the principal
structures referred to in routine descriptions of land and freshwater
molluscs can be accessed via the Terminology toolbar button. 
#22. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs, and instructions for
counting shell whorls, can be accessed via the Terminology
toolbar button. 
#23. '\i{}Sinistral\i0{}' (left-handed) versus '\i{}dextral\i0{}'
(right-handed) is readily ascertainable with reference to the direction
of coiling of univalve shells. To assign one, hold it vertically with
its spire on top, the umbilicus (if there is one) below, and the
aperture towards you. The aperture of a dextral shell will then lie to
the right of the median axis, that of a sinistral one to the left.
\par{}Many spiral-shelled species are liable to mutations that result in
reversal of the direction of convolution, which involves the disposition
of the internal organs as well as sinistrorsity or dextrorsity of the
shell. Dextrorsity is much the commoner normal condition, but
sinistrorsity characterizes Clausiliidae, Physidae and some
Vertiginidae. The depressed spire of Planorbidae is not readily
distinguishable from the umbilicus, but they are also correctly
interpreted as sinistral with reference to the viscera. \par{}Reversed
individuals, which have sometimes attracted varietal status, are usually
rare, but they seem to be commoner in some species than others; and in
some cases (exemplified in \i{}Lymnaea peregra\i0{}) the mutant
sinistral condition is heritable, and viable to the extent that
populations can persist for many years. \par{}Illustrations of the
principal structures referred to in routine descriptions of land and
freshwater molluscs can be accessed via the Terminology toolbar
button. 
#25. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs, and instructions for
measuring heights and widths of shells, can be accessed via the Terminology'
toolbar button. 
#26. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs, and instructions for
measuring heights and widths of shells, can be accessed via the Terminology toolbar button. 
#30. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs, and instructions for
measuring heights and widths of shells, can be accessed via the Terminology toolbar button. 
#31. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs can be accessed via the
Terminology toolbar button. 
#32. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs, and instructions for
measuring heights widths of shell components, can be accessed via the
Terminology toolbar button. 
#33. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs can be accessed via the
Terminology toolbar button. 
#34. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs, and of the terminology
adopted here to describe shell shapes, can be accessed via the Terminology toolbar button. 
#35. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs, and of the terminology
adopted here to describe shell shapes, can be accessed via the Terminology toolbar button. 
#36. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs, and of the terminology
adopted here to describe shell shapes, can be accessed via the Terminology toolbar button. 
#37:40-42:44-46. Illustrations of the principal structures referred to
in routine descriptions of land and freshwater molluscs can be accessed
via the Terminology toolbar button. 
#47. \i{}Umbilicus\i0{}: a cavity at the base of those whorled, univalve
shells in which the whorls do not form a solid axis. \par{}Illustrations
of the principal structures referred to in routine descriptions of land
and freshwater molluscs can be accessed via the Terminology
toolbar button. 
#48-49. Illustrations of the principal structures referred to in routine
descriptions of land and freshwater molluscs can be accessed via the
Terminology toolbar button. 
#55. This obviously useful character calls for judicious application for
identification, with due regard to the habitat - water snails can be
emergent in wet conditions, and many are equipped to withstand seasonal
desiccation.
#64-65. Information on love darts, along with good illustrations, is
available on the internet at: 
http://en.wikipedia.org/wiki/Love_dart#Occurrence_within_the_pulmonate_snails_and_slugs

 
