Exploring the Intertidal

Check out the intertidal zone and its biodiversity!

Mollusca

Molluscs are one of the largest animal phylums, with between 50000-110000 species! Octopus, squid, snails, nudibranchs, and bivalves are all molluscs. There is much diversity in this group, but most members have a shell made of calcium carbonate set in a protein matrix. The shell is made of three layers: the outer, organic periostracum, the middle, calcareous prismatic layer, and the calcareous inner nacreous layer. The shell is secreted by a tissue called the mantle. Most molluscs also have a muscular "foot" that is used for locomotion.

Class Gastropoda

The "inside scoop" of a typical gastropod, or snail-type of mollusc.

Snails and nudibranchs belong to the Class Gastropoda. Gastropods are diverse in terms of habitat and biology. Because they are often slow moving, many have well-adapted chemical and behavioural responses to predators. The columellar muscle retracts the soft body into the shell, and a hard proteinaceaous disc called the operculum functions as a trap door.

Class Bivalvia

The Class Bivalvia includes clams, mussels, oysters and scallops. Bivalves have a hinged shell with two valves and a spacious interior (mantle) cavity. They are usually sedentary and filter or deposit feed. Siphons are used for the inflow and outflow of water, and these can be extended for some distance, so that the bivalve can hide underground away from predators.

Mytilus californianus (California Mussel)
Description: Blue/black in colour, often with a streak of brown. Ridged surface.
Range: Alaska to Mexico
Habitat: Exposed rocky intertidal.
Cool Fact: Females can produce 100 000 eggs/year! Attached to rocks with tough strands called "byssus threads".

Mytilus trossulus (Pacific Blue Mussel)
Description:  Blue/black. Smaller and smoother than the California mussel.
Range: Alaska to Mexico
Habitat: Sheltered rocky intertidal to 40m subtidal.
Cool Fact: Also attached to rocks with byssus threads.

Ostrea lurida (Native Pacific Oyster)
Description: Irregular, oval shape. Grayish-white in colour with brown or purple rays. Rough, scaly surface.
Range: Alaska to Baja, California.
Habitat: Attached to rocks and pilings. Low intertidal, shallow subtidal.
Cool Fact: Switches from male to female each year.

 Protothaca staminea (Pacific Littleneck Clam)
Description:  Roundish shells. Often with a brown zig-zag pattern.
Range: Aleutian Islands, Alaska to southern California.
Habitat: Sand and gravel beaches. Mid-intertidal to 18m subtidal.
Cool Fact: Can burrow 10cm under the surface.

Class Gastropoda

Hermissenda crassicornis (Opalescent nudibranch)
Description: Brightly coloured in yellow and green. Orange markings on back and blue stripe on sides.
Range: Alaska to Mexico
Habitat: Mud flats, eel grass beds, docks and rocky intertidal.
Cool Fact: Eats small cnidarians and uses their nematocysts (for more info see the Cnidarian Page).

Littorina scutulata (Checkered Periwinkle)
Description:  Brown or black shell. Elongated spire.
Range: Alaska to California.
Habitat: On seaweed (especially Fucus sp.) and rocks in the high and mid intertidal.
Cool Fact: Land snails may have evolved from this species!

Littorina sitkana (Sitka Periwinkle)
Description:  Black, brown, or white shell. Rounder than L. scutulata and with definite raised ridges.
Range: Alaska to Puget Sound, Washington.
Habitat: On seaweed and rocks, throughout the entire intertidal.
Cool Fact: Can survive out of the water for long periods and will actually drown if submerged for too long!

Nucella emarginata (Striped Dogwinkle)
Description:  From striped grey and yellow to solid, bright orange.
Range: Bering Sea to Mexico
Habitat: Rocky intertidal. Often found in mussel and barnacle zones.
Cool Fact: Carnivore that drills holes in the shells of other molluscs in order to eat them.

Olivella biplicata (Purple Olive)
Description: Varies from white to purple. Smooth, shiny shell.
Range: Sitka, Alaska to Baja, California
Habitat: Sandy beaches, low intertidal to 46m subtidal.
Cool Fact: These shells were used as money and jewelry by west coast First Nations.

Tegula funebralis (Black Turban Snail)
Description: Black shell, often worn through at the top to show white in older snails.
Range: British Columbia to lower California.
Habitat: Rocky high to mid intertidal.
Cool Fact: This snail can live to 100 years old!

check out the scallops, sea slugs, nudibranchs,
and Gum Boot chiton pages!

---

 to Intertidal Field Guide directory