Gemma gemma (Totten) - Shell no longer than high, slightly triangular; general color white with purple tinge, shell very thin, hinge and teeth very reduced. Introduced to the San Francisco Bay from the east coast. This bivalve is a filter feeder, meaning that it takes in water and "filters" the algae from it to digest. It is considered a primary consumer.

Macoma nasuta (Conrad) - Also called the bent-nosed macoma. Lives in shallow water with muddy bottoms. Some are 2 inches long, color grayish white with thin shell. Anterior end broadly rounded; posterior end bluntly pointed, partially truncated and noticeably bent to one side and is a filter feed like G. gemma.

Mytilus edulis (Linne) - Shell elongated -triangular, rather plump, with scarcely noticeable beaks at the apex. Length about 3 inches on the average. Adult shells are deep bluish black with a shiny periostracum (outer covering); juveniles show various shades of gray, green and brown, often exhibiting rays of color. Also called the bay mussel, lives in rock areas in colonies. M. edulis is a filter feeder with very few natural enemies.

Iscadium demissum - Also known as the ribbed horse mussel has fine ribbed lines running lengthwise. This purple mussel grows to 3.5 inches. Pearly luster inside of shell.

Ostrea lurida Carpenter - No longer than 2 inches, the shape quite irregular, depending on the surface of the object on which it grows. Shells are not especially thick or heavy. Lives in shallow waters with stony bottoms. This is a common native oyster along the west coast and is also a filter feeder.

Tapes japonica (Deshayes) - Also called the Japanese Littleneck clam is about 2 inches long. It is an introduced species from Japan. It has ribs with yellowish gray color in a chevron pattern, running up and down their shell.

GASTROPODS

Ocenebra interfossa (Carpenter) - A spindle-shaped shell about 3/4 of an inch high. There are 5 whorls, high spiral, and a sharp apex. Lives in the shoreline or on rocks. Commonly called the sculptured rock shell, because of the large wavy ridges that revolve with the whorls. This little gastropod is top of the food chain in the mud, eating many of the bivalves and other gastropods.

Nassarius obsoletus (Say) - Black Dog Whelk; medium sized, surface blackish with obscure spiral and longitudinal lines, introduced and extremely abundant in the San Francisco Bay (mud snail), nearly one inch high, with about 6 whorls. Apex rather blunt, and commonly more or less eroded. The only sculpture consists of weak revolving lines, plus a few vertical folds on the early whorls. Inner lip deeply arched. Color deep purplish black. This is an east coast snail, probably introduced into California water with young oysters. It is a scavenger that eats dead fish or other organic debris.

Nassarius tegulus (Reeve) - Commonly called the Mud Dog Whelk. Lives in the mudflats, about 3/4 of an inch high, a stocky shell of 5 or 6 whorls with a sharply pointed apex. Sculpture of weak revolving lines, sometimes faintly banded. Inner lip broadly expanded, outer lip thickened. This group eats similar to N. obsoletus and is hard to distinguish between the two.

Cerithidea californica Halderman - Greatly elongated, with approximately 10 rounded whorls. Sculptured with vertical ribs and revolving ridges, aperture open. Color is brown. Shell is approximately 1.5 inches high. A large group of organisms that live mainly in tropical waters. A few will venture into the San Francisco Bay, but this group is very rare. This groups eats similar to N. obsoletus.

Acmaea digitalis Eschscholz - Finger Limpet is the common name for this species. Color is gray with stripes, specks and blotches of brown and white. Dark brown to black border at rim. Shells conical, oval, and open at base, with no opening at the top. No spiral at any stage of growth and does not have the pearly look to its inside shell. They live on stones and grasses at the shoreline, generally between the tide limits. They are herbaceous which means they eat small algae or bacteria.

HOW CAN WE TELL WHO EATS WHO?

Notice the tiny little round hole that are in each of the shells above. This is where a carnivore (usually a gastropod) drills into the shell and then "sucks" its dinner out. One of the gastropods above has also been punctured. Another species of gastropod can feed on another species.