These creatures are all of the order Gastropoda - having a single, often coiled, shell, as opposed to the bivalves, which have two matching shells. Most snails are hermaphroditic. Also, most snails have a right-hand twist to the shell, although there are exceptions.
Nudibranchs are a form of snail that has lost its shell, while Corollas and Sea Butterflies are snails that have abandoned not just their shells, but the snail-like existence entirely, swimming up into the water column as plankton.
X-ray image of a Channeled Whelk, showing internal structure.
Size: to 8"
Habitat: intertidal down to 60 ft
Whelks are the largest snails in this area. Related Lightning Whelk grows to 16", and is sometimes called Conch and eaten as such. Whelks prey on bivalves by drilling through their shells.
A large ( and filthy ) whelk feeding on something. The head end is to the left.
Upended and fully withdrawn, showing the operculum which closes-off the shell. This
individual was about the size of your hand. Note the curious puffer fish at upper-right.
See Restrictions and Health Advisories for catch limits.
Size: to 4"
Habitat: generally in deeper water, but possible in shallows
Notes: quite common in places
These snails are responsible for the curious sand collars that divers often find. They produce a glue to cement the sand grains together into a protective ring for their eggs. Moon Snails are predators of other shellfish, which they smother with their enormous foot. They are themselves sometimes eaten as Scungilli.
Size: to 1"
Habitat: intertidal to shallows, on muddy bottoms
This scavenger is often found on dead fish and other animals.
Size: to 1"
Habitat: subtidal down to 50 ft
Notes: This little snail uses acid and its rasp-like tongue to drill a neat hole in a bivalve or barnacle victim, then sucks out the contents.
Size: to 1.2"
Habitat: intertidal, on any solid substrate
Notes: vegetarian - feeds on seaweeds
This is another good snail for a cold-water aquarium, as it will constantly clean all surfaces of algae, and also consume any other waste it finds. They are also edible.
Size: to 0.8 - 2 "
Habitat: attached to solid surfaces, often other larger shells
Although the dead empty shells superficially resemble bivalves, Slipper Shells are actually extremely flattened snails. The living animal has only a single uncoiled shell, and lives under it attached to a hard surface. A small shelf inside gives these odd animals their name. The illustration shows the shell from above on the left and from below on the right. Slipper shells are quite commonly attached to the undersides of Sea Scallops, often in stacks. Filter feeders.