Bivalves

The "Blue Mussel" was once considered to be a single species. At least three distinct species have been identified, all of which,
may be found in the Pacific Northwest - Mytilus trossulus, M. edulis and M. galloprovincialis. These smooth-shelled Blue Mussel
species have been spread around the world, in part, the result of over 500 years of shipping activity. They have also been introduced
in commercial ventures. In some locations the species readily hybridize with each other. The full extent of the spread of each
species and their hybridization is yet unknown. This further confuses a group which is already virtually indistinguishable from each
other. All three species may be blue, black or brown in color. We refer to this group as the "Mytilus complex" on our lists where the
exact species cannot be determined. Mytilus trossulus is the species native to the Pacific Northwest and therefore predominates in
most places.

Mytilus trossulus
Gould, 1850
Foolish Mussel *
intertidal to 5m size to 90mm
central California to north Alaska,
across the Arctic to northern Europe
It is very common but cannot be
readily distinguished by shell
alone from M. galloprovincialis.
(photo is an Alaskan specimen)

Mytilus edulis Linnaeus, 1758
Blue Mussel
intertidal to 5m size to 115mm
There is experimental mariculture of this
species in BC. It is unsure if it has
been introduced in the wild. It is present on
both sides of the Atlantic Ocean and on both
coasts of South America.
(photo is a specimen from the northeast U.S.)

live individual - intertidal cluster - subtidal

Modiolus modiolus (Linnaeus, 1758)
Northern Horsemussel
intertidal to 200m size to 23cm
circumpolar reaching south to southern California, Japan, New Jersey, and the Meditteranean
It is not commonly found intertidally. It prefers a gravel/sand substrate and tends to live in
clusters. Look for the orangish flesh, visible in submerged specimens.
It often hosts pea crabs.

Musculista senhousia
(Benson, 1842)
Japan Mussel or Green Mussel
intertidal to 20m size to 35mm
introduced from Japan with oyster seed,
populations now established from southern
BC to southern California
It can readily be found in the areas it
has populated. It has a thin shell which
ranges from green to red, with dark
brown wavy lines. It prefers estuaries.

Adula californiensis (Philippi, 1847)
California Datemussel
intertidal to 20m size to 60mm
southern California to Haida Gwaii, BC
It is not uncommon, but takes some effort
to find. It bores into clay, shale and other
soft rocks.

Musculus discors (Linnaeus, 1767)
Discordant Mussel
intertidal to 150m size to 55mm
Panarctic and circumboreal, reaching to central Washington, northern Japan, New York and the Mediterranean
It is rarely found intertidally. The periostracum is olive-green to dark brown. The shell shape and sculpture are variable. There is a distinct fold separating the central and posterior regions.
(previous names - Musculus laevigata, Musculus substriata)

live specimen showing byssal threads intertidal in sand siphon as seen subtidally

Modiolus rectus (Conrad, 1837)
Straight Horsemussel *
intertidal to 15m Peru to Haida Gwaii, BC size to 230mm
It can be found intertidally. It prefers sand and mud and specimens tend to be solitary. The shell is very
elongate and the periostracum is thick and adherent. The distinct light and dark portions of the shell are typical.

live individual mussel bed

Mytilus californianus Conrad, 1837
California Mussel *
intertidal to 100m northern Mexico to southern Alaska size to 255mm
It is common on exposed coastlines. The shells are thick with strong radial ribs and a
thick blue-black periostracum.

Mytilus galloprovincialis
Lamarck, 1819
Mediterranean Mussel
intertidal to 5m size to 150mm
It is bred commercially and has been
introduced in the wild to portions of the west
coast. It forms hybrids with M. trossulus in
central California but its breeding status in the
Northwest is uncertain. It is native to Europe
and has been introduced throughout the world.
It cannot be readily distinguished by shell
alone from M. trossulus.
(photo is a specimen from a commercial grower)

Family Mytilidae