Species Descriptions


 
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In the descriptions below, "Size" refers to shell length only and only gives the largest average size for the given species.

Mytilus trossulus  (Gould, 1850)  Blue Mussel
 
Size:
to 110 mm
Range: 
N. Alaska to N. California
Habitat:  
Usually found in quiet bays but also occurs along the outer coast along with Mytilus californianus (the California Mussel).  Normally found through the intertidal-zone to a depth of 5 m.  The preferred substrate is rock, wood or some other solid structure.
Misidentification:
Sometimes this mussel is mistaken for M. californianus (California Mussel) or M. edulis (Bay Mussel).
Life History:  
This species spawns when water temperatures reach 12o C, around May, where the females release three to six million eggs into the water column.  After living planktonically for approximately four weeks, the larvae settle out on algae encrusted substrate and metamorphose into the adult form.  M. trossulus, like  M. californianus and M. edulis, form dense mats along the intertidal zone.  As silt deposits increase within these mats, those mussels in the center will move or "crawl" to the outside of the mat to prevent their being buried and smothered.
Predators: 
Pisaster spp. and Nucella emarginata

Mytilus galloprovincialis (Lamarck, 1819)  Mediterranean Mussel
 
Size:
to 90 mm
Range:
S. California to Mexico, commercially grown in Totten Inlet, Washington, and found in sheltered inlets of British Columbia, Canada
Habitat:
Same as Mytilus trossulus
Misidentification:
Mytilus trossulus, M. edulis
Life History:
An introduced species, it is indigenous to the Mediterranean Sea, W. France Britain and Ireland.
Predators:
Pisaster spp.

Mytilus edulis (Linnaeus, 1758)  Blue Mussel, Bay Mussel

Size:
to 110 mm
Range:
Uncertain at this time, introduced to British Columbia, Canada but indigenous to the Atlantic Coast.
Habitat:
Intertidal to 5 m on solid substrates like rock or wood in quiet waters
Misidentification:
Mytilus trossulus, M. galloprovincialis
Life History:
An introduced species, it can live up to 2 years.  Very hearty, it requires periods of desiccation and needs less O2 than other Mytilids.  This species is very close in appearance to M. trossulus and it is nearly impossible to visually distinguish the two apart.  The difference is enzymatic and laboratory examination is required to determine which is which if identities are in dispute.
Predators:
Sea Birds, Pisaster spp., Nucella emarginata

Modiolus modiolus  (Linnaeus, 1758) Horse Mussel, Northern Horse Mussel
 
Size:
to 180 mm
Range:
Bering Sea to S. California
Habitat:
Prefers to live in quiet bays, intertidal to 200 m, buried in soft, gravely mud or sand in Puget Sound, or attached to rocks elsewhere.
Misidentification:
Life History:
This species lives up to 20 years and can survive sub-0o C for several days.
Predators:
Polinices lewisii

Crassostrea gigas (Thunberg, 1793)  Pacific Oyster, Japanese Oyster
 
Size:
to 300 mm
Range:
Alaska to California
Habitat:
Rocky, solid substrates.  Commercially grown on firm mud flats.  Intertidal to 6 m.  Larvae prefer to settle out on adult oyster shells.
Misidentification:
Life History:
An intentionally introduced species.  Spawning occurs when water temperatures exceed 18o C (from June to September).  Unlike most bivalves, the eggs do not exit the shell via the siphons but are released into the suprabranchial chamber where they are expelled from the gills by a contraction of the adductor muscles.  This species matures in one year and can live up to twenty years.
Predators:
Cancer spp., Nucella emarginata, Pisaster spp.

Ostreola conchaphila ()  Olympia Oyster, Native Oyster
 
Size:
to 50 mm
Range:
Alaska to Panama
Habitat:               
On rocky substrates near the low tide line or on mud flats and gravel bars in quiet bays with low salinities.
Misidentification:
Pododesmus cepio
Life History:
Formerly very abundant, this species has now been widely displaced by the commercially introduced and much larger, Crassostrea gigas or wiped out by land filling, dredging or pollutants in their environments.
Predators:
Nucella emarginata, Pisaster spp.

Pododesmus cepio (Gray, 1850)  Jingle shell, Rock Oyster
 
Size:
to 130 mm
Range:
Bering Sea to S. California
Habitat:
Rocks and other solid substrates, intertidal to 90 m.
Misidentification:
Life History:
The greenish tint of the shell interior is due to algae living within the shell lattice.  This color is retained even after death.
Predators:
Pisaster spp.

Chlamys rubida (Hinds, 1845)  Pink Scallop, Smooth Pink Scallop
 
Size:
to 66 mm
Range:
S. Alaska to S. California
Habitat:
Subtidal from 1 to 200 m on muddy or gravely substrates.
Misidentification:
Chlamys hastata
Life History:
A free swimming species, the approach of a predator can elicit an impressive escape response as the scallop claps its valves together and jets away to safety.
Predators:
Pisaster spp., Evasterias spp.

Chlamys hastata (Sowerby, 1842)  Spiny Scallop
 
Size:
to 83 mm
Range:
S. Alaska to S. California
Habitat:
Subtidal from 2 to 150 m on rocky reefs.
Misidentification:
Chlamys rubida
Life History:
Free swimming, although this species may attach to rocks by way of byssal threads.
Predators:
Pisaster spp., Evasterias spp.

Hinnites giganteus (Gray, 1825)  Giant Rock Scallop, Purple Hinged-Rock Scallop
 
 
 
Size:
to 250 mm
Range:
N. Alaska to S. California
Habitat:
Intertidal to 80 m.  Found mainly on rocky substrates in deep water rarely found under boulders in the intertidal zone.
Misidentification:
Juveniles may be mistaken for Chlamys hastata or C. rubida.
Life History:
Free swimming as a juvenile, Hinnites giganteus, becomes permanently attached to the substrate as it matures.  This species can live up to 20 years and, with the exception of Patinopecten caurinus (not described at this site), is the largest scallop species in the world.
Predators:

Clinocardium nuttallii (Conrad, 1837)  Heart Cockle, Nuttal's Cockle, Basket Cockle
 
Size:
to 140 mm
Range:
Bering Sea to S. California
Habitat:
Intertidal to 30 m, sandy gravel in sheltered bays where the salinity doesn't vary much.
Misidentification:
Life History:
Unlike most bivalves, C. nuttallii is hermaphroditic.  Maturity is reached in two years and they can live up to sixteen years.  Spawning occurs from June to July.
Predators:
Pycnopodia spp., Pisaster spp. elicits an escape response.

Tresus capax (Gould 1850)  Horse Clam, Gapper Clam
 
Size:
to 180 mm
Range:
Gulf of Alaska to Central California
Habitat:
Muddy sand, dense sand, silty sand and gravel in protected bays.  Burrows down to 60 cm. Intertidal to 30 m.
Misidentification:
Tresus nuttallii, Mya arenaria, Panope abrupta
Life History:
Spawning occurs when the water begins to warm up and may spawn more than once in a season. T. capax may live up to 12 years.  This species commonly hosts the commensal pea crab, Fabia subquadrata, in southern Puget Sound.
Predators:
Polinices lewisii, Cancer magister, Pisaster spp.

Macoma secta (Conrad, 1837)  White Sand Macoma
 
Size:
to 100 mm
Range:
British Columbia, Canada to California
Habitat:
Intertidal to 50 m.  Prefers sandy substrates in sheltered waters, burrowed up to 20 cm deep.
Misidentification:
Macoma inquinata, Macoma nasuta
Life History:
Unlike most bivalves, Macoma secta is not a suspension filter feeder but a deposit filter feeder. Its siphons are separated.  The inhalant siphon takes up detritus and organic matter directly from the substrate while the exhalant siphon deposits the indigestible particles and sediment elsewhere.
Predators:
Polinices lewisii

Macoma nasuta (Conrad, 1837)  Bent Nosed Clam
 
Size:
to 70 mm
Range:
Alaska to S. California
Habitat:  
Intertidal to 50 m.  Prefers mud to muddy sand substrates situated in quiet waters and can burrow down to 15 cm.
Misidentification:
Macoma secta, Macoma inquinata
Life History:
A dioecious species that spawns in early summer.  Unlike most bivalves, Macoma nasuta is not suspension filter feeder but a deposit filter feeder. Its siphons are separated; the inhalant siphon takes up detritus and organic matter directly from the substrate while the exhalant siphon deposits the indigestible particles and sediment elsewhere.
Predators:
Shore birds, Polinices lewisii, Pisaster spp., Cancer productus, Cancer gracilis, Cancer magister

Macoma inquinata (DeShayes, 1854)  Irus Clam, Pointed Macoma
 
Size:
to 55 mm
Range:
Alaska to California (rarely found south of Santa Barbara)
Habitat:
Intertidal to 50 m.  Prefers substrates of soft, muddy sand and eel grass beds in protected waters
Misidentification:
Macoma secta, Macoma nasuta, Mya arenaria
Life History:
Unlike most bivalves, Macoma inquinata is not suspension filter feeder but a deposit filter feeder.  Its siphons are separated.  The inhalant siphon takes up detritus and organic matter directly from the substrate while the exhalant siphon deposits the indigestible particles and sediment elsewhere.
Predators:
Shore birds, Polinices lewisii, Pisaster spp.

Saxidomus giganteus (DeShayes, 1839)  Butter Clam
 
Size:
to 130 mm
Range:      
Bering Sea to Central California
Habitat:
Intertidal to 40 m, buried to 30 cm.  Prefers quiet bays and estuaries with muddy sand or muddy/sandy gravel.
Misidentification:
Tresus capax
Life History:
Spawns in the Fall when water temperatures reach 11.5 to 18o C.  This species can live up to 20 years.
Predators:
Polinices lewisii, Nucella emarginata

Protothaca tenerrima (Carpenter, 1857)  Thin-shelled Littleneck
 
Size:
to 110 mm
Range:
British Columbia, Canada to S. California
Habitat:
Intertidal to 10 m in gravely sand.
Misidentification: 
Saxidomus giganteus, Protothaca staminea
Life History:
Predators:
Polinices lewisii

Protothaca staminea (Conrad, 1837)  Native Littleneck, Steamer Clam
 
Size:
to 75 mm
Range: 
Aleutian Isles. to Mexico
Habitat:
Intertidal to 37 m.  Prefers coarse sand but may be found in cobble or coarse shell mixed with gravel mud or sand buried to depths of 80 mm.  Primarily estuarine but can occasionally be found along the open coast.
Misidentification:
Tapes philippinarum, Protothaca tenerrima
Life History:
Matures in the second year and spawns from April to July.  Though normally dioecious, there is some occurrence of hermaphrodism in P. staminea.  Not a strong digger, this species can not move vertically very well but can dig horizontally quite well.
Predators:
Ceratostoma spp., Nucella emarginata, Polinices lewisii, Pycnopodia spp., Evasterias spp., Pisaster spp., Cancer productus

Tapes philippinarum (Adams and Reeve, 1850)  Manila Clam, Japanese Littleneck
 
Size:  
to 75 mm
Range:
Northern British Columbia, Canada to California
Habitat: 
Intertidal to 10 m.  Preferring shelly or gravely mud or sand on low energy, stable beaches
Misidentification:
Protothaca staminea
Life History:
An introduced species,  accidentally arriving with the commercial importation of Crassostrea gigas and now supplanting the native Protothaca staminea.  Maturing when the shell reaches 15 mm this species spawns once per year between May and September when the water temperatures exceed 15o C.
Predators: 
Polinices lewisii, Pisaster spp., Cancer spp.

Mya arenaria (Linnaeus, 1758)  Eastern Soft-shell Clam
 
 
Size: 
to 110 mm
Range:      
S. British Columbia, Canada to S. California
Habitat: 
Intertidal to 9 m in muddy or sandy bays and estuaries buried up to 30 cm deep.
Misidentification: 
Tresus capax, Saxidomus giganteus
Life History:   
An accidentally introduced species, believed to have been brought over with Crassostrea virginica spat introduced commercially to San Francisco Bay in 1869, it is indigenous to the Atlantic Coast and Europe although there is evidence in Pliocene fossil records that this species did at one time occur naturally along the East Pacific coast.  Mya arenaria has two spawning seasons.  One in the fall and the other in the spring.  The male spawns first which signals the females to spawn.  All life stages of this species are estuarine.  After reaching maturity this species outgrows its foot and ceases to dig.
Predators: 
Raccoons, shore birds, Pisaster spp.

Panope abrupta (Conrad, 1849)  Geoduck, King Clam
 
Size:   
to 195 mm (shell only, entire animal can exceed 1 m when extended)
Range: 
Alaska to California, most abundant in Puget Sound and Straight of Georgia.
Habitat: 
Intertidal to 100 m+.  Prefers soft mud, pea gravel, stable mud and sand substrates in bays, sloughs, and estuaries burrowing up to 100 cm deep.
Misidentification:
Life History:  
The largest burrowing clam in the world, this species can live to be over 120 years old.  Like Mya arenaria, after reaching maturity (60-100 mm for males and 100-120 mm for females) Panope abrupta out grows its foot and stops burrowing.  This species spawns once a year between April and July.
Predators:  
Pisaster spp., Pycnopodia helianthoides, the siphon tips are eaten by Leptocottus armatus the Pacific Staghorn Sculpin.

Bankia setacea (Tyron, 1863)  Shipworm, Feathery Shipworm
 
Size:  
to 7 mm (shell only; entire animal can exceed 1 m)
Range: 
Bering Sea to S. California
Habitat:    
Intertidal to 90 m.  Found boring into wood substrates.
Misidentification:
Life History: 
All larvae start out as male and, later, about half develop into females.  Spawning occurs during January.
Predators:



 
MAIN
BIOLOGY
KEY
SPECIES
LIST
GLOSSARY
MOLLUSCAN
LINKS
LITERATURE
CITED


Page author: Brian L. Kegel  kegelb@elwha.evergreen.edu
Last modified: 980906