This class, containing over 35,000 living and 15,000 fossil gastropod species, comprises the largest class of Mollusca, and includes the limpets, top shells, periwinkles, slipper shells, snails, slugs, sea hares, abalones, nudibranches, or sea slugs, and sea butterflies. Gastropods are primarily marine, but freshwater and terrestrial forms occur. When present, the typical gastropod shell is a three-layered, spiral whorl of calcium carbonate, which varies in color, shape, ornamentation, and size according to the species. Within this shell is the tall, coiled body mass. Some forms, such as slugs, are shell-less and do not have a tall body mass. Gastropod larvae undergo a twisting, or torsion, that brings the rear of the body (mantle cavity, gills, and anus) to a position near the head and results in the twisting of internal organ systems. In many this twisted form is retained by the adult; in others it is partially lost.

There are three subclasses: the Prosobranchia, which contains the majority of gastropods; the Pulmonata, which contains the land snails; and the Opisthobranchia, which includes the sea hares and sea slugs. The latter subclass consists of animals with reduced shells or none at all. Most gastropods are motile, but some, e.g., the slipper shell ( Crepidula ), are sedentary. Some, such as the sea butterflies, swim, and others, including the terrestrial snails, move by means of a well-developed foot.

EXIF Data

Camera Type: NIKON D3100
Lens: 18.0-55.0 mm f/3.5-5.6
Date Taken: 4/5/13
Aperture: f/11.0
Shutter Speed: 1/80
ISO: 200
Exposure Mode: Manual
Focal Length: 55.0 mm
White Balance: Manual
Metering Mode: Center Weight
Light Source (In Camera): N/A
Flash: N/A
Light Source (External): Cloudy weather
Size: 273 KB
Location: 4361 Custis Avenue, Sacramento, California
Latitude: 38,32.7424N
Longitude: 121,29.8172W
Elevation: 7.70 m