San Diego Natural History Museum--Your Nature ConnectionSDNHM Biodiversity Research Center of the Californias - Marine Invertebrates

Souvenirs from the Sea. What kind of shell is this? Sometimes our most unique treasures are the most common. Along the beaches of the long, winding California coastline beachcombers can gather souvenirs. These natural treasures—shells of different colors, shapes, and sizes—help us recall the stunning beauty of the California shore, and of special moments passed there.

It is fun to find shells on our local beaches, and it is even more interesting to also observe mollusks (as the living shells are known) naturally occurring in their habitat. When observing living mollusks in their environment, be sure to follow steps to protect them: at rocky beaches, turn back rocks after looking under them; at sandy beaches, place clams and other burrowing animals in the same position you found them; and at salt marshes, only observe organisms at the edge of the marsh to avoid trampling sensitive plants.


Following are examples of different marine habitats that occur along the San Diego shore, and some shell species that are found associated with these habitats. About half of the species shown here only occur in southern California and south to Mexico. The rest have wider ranges, and occur into northern California and beyond. (To find out what kind of marine habitats existed in San Diego a few million years ago, read "The Elusive Pliocene Rocky Shore.")


Rocky Shores provide a lot of structure for a great variety of marine organisms. California Mussels attach strongly to rocks with byssus cords and can withstand the beating of the waves. Smaller snails like the Checkered Periwinkle and the Angular Unicorn must seek shelter under rocks and in cracks. Others, such as the Festive Murex and the Wavy Turban are more common in calmer, shallow water, and may also be found inside bays such as Mission Bay.
The snail shell featured in the title, Souvenirs from the Sea, is the Angular Unicorn, Acanthina spirata (Blainville, 1832), which lives on rocky shores among barnacles and mussels. The common name comes from a tooth on the lip of the shell, which the snail uses to prey on barnacles.

California Mussels on rocks of Ocean Beach jetty, photo by Scott Rugh  California Mussel shells, photo by Lollo Enstad Left: California Mussels on rocks of Ocean Beach jetty
Right: California Mussel shells, Mytilus californianus (Conrad, 1837).



Sandy Shores do not provide a solid bottom, yet many species are able to prosper in the shifting sands. Large clams, such as the Pismo Clam, are held down by the weight of their massive shells. The Pacific Razor Clam finds refuge by burrowing very deeply. Snail species, such as the Channeled Nassa and the Purple Dwarf Olive, have a very large foot that helps them dig quickly, and stay on the bottom.

Purple Dwarf Olive, photo by Lollo Enstad and live Purple Dwarf Olive burrowing in the sand, photo by Scott Rugh  Pismo Clams, photo by Lollo Enstad Left: Purple Dwarf Olive, Olivella biblicata (Sowerby, 1825) shells
Center: live Purple Dwarf Olive burrowing into sand at Mission Bay
Right: Pismo Clams, Tivela stultorum (Mawe, 1823), striped varieties.

Estuary and Soft-rock Reef Shells >>

Text by Scott Rugh, Collections Manager, Invertebrate Fossils; photos by Scott Rugh and Lollo Enstad