Invasion History

First Non-native North American Tidal Record: 1924
First Non-native West Coast Tidal Record: 1924
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

The native range of Neotrapezium liratum is from the Russian Far East to Vietnam, including the coasts of Japan, China, and Korea (Huang 2001; Kil et al. 2005; Academy of Natural Sciences of Philadelphia 2006; Kolpakov and Kolpakov 2013). It was introduced to coastal waters of Washington and British Columbia with Pacific Oysters (Crassostrea gigas) from Japan (Carlton 1979; Carlton 1992).

North American Invasion History:

Invasion History on the West Coast:

Neotrapezium liratum was discovered in Samish Bay, Washington (WA) growing among planted Pacific Oysters in 1924 (Kincaid 1947, cited by Carlton 1979). However, no reproduction was seen there, or in a later occurrence in Ladysmith Harbor, British Columbia (BC) (Kincaid 1947, Carl and Giguet 1958, both cited by Carlton 1979). Breeding populations do occur in Willapa Bay, WA (Kincaid 1947, cited by Carlton 1979; Cohen et al. 2001) and Boundary Bay, BC (Gillespie et al. 2007). This bivalve was abundant in some locations in Willapa Bay (Cohen et al. 2001) and may be overlooked in others.


Neotrapezium liratum is a small bivalve (adults are ~25-60 cm long), with a roughly rectangular shell, laterally compressed. The umbo is located near the anterior end of the shell and is moderately prominent. The shell has prominent concentric growth lines and radial markings running from the umbo to the posterior edge of the shell. The inner margin is smooth. A strong dorsal keel extends posteriorly from the umbones. The periostracum has radial rows of bristles.The color is light to dark brown, with white areas. The interior of the shell is pearly, with radial streaks. This bivalve dwells in crevices in the intertidal zone (Abbott 1974; Coan et al. 2000; Eissinger 2009; Kondo et al. 2009).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Bivalvia
Subclass:   Heterodonta
Order:   Veneroida
Superfamily:   Arcticoidea
Family:   Trapezidae
Genus:   Neotrapezium
Species:   liratum


Cypricardium liratum (Reeve, 1843)
Trapezium (Neotrapezium) liratum (Reeve, 1843)
Trapezium japonica (Pilsbry, 1905)

Potentially Misidentified Species



Neotrapezium liratum is a small bivalve, reaching 53 mm in length, but usually smaller (Eissinger 2009). We have no information on the reproduction of this species. Neotrapezium liratum settles in cracks and crevices in rocky areas, oyster reefs, eelgrass beds, etc., where it s attached by its byssi (Coan et al. 2000). Its shape may vary dependent on the availability of space within its chosen habitat (Eissinger 2009; Kondo et al. 2009). It often occurs in estuaries, in waters of varying salinity, and in the mid-upper intertidal. In Willapa Bay, Washington it was found at 1-20 PSU and at sites exposed at low tide (Cohen et al. 2001).



Trophic Status:

Suspension Feeder



General HabitatOyster ReefNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatGrass BedNone
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)-1Field, Kolpakov and Kolpakov 2013
Maximum Temperature (ºC)29Field, Kolpakov and Kolpakov 2013
Minimum Salinity (‰)1Field salinity, Willapa Bay (Cohen et al. 2001)
Maximum Salinity (‰)NoneNone
Maximum Length (mm)60Kondo et al. 2009
Broad Temperature RangeNoneCold temperate-Tropical
Broad Salinity RangeNoneOligohaline-Euhaline

General Impacts

The bivalve Neotrapezium liratum is established in Boundary Bay, British Columbia (Gillespie et al. 2007) and is locally abundant in Willapa Bay, Washington (Cohen et al. 2001). However, no impacts are known.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
EAS-I None 0 Native Estab
NWP-2 None 0 Native Estab
NWP-3b None 0 Native Estab
NWP-3a None 0 Native Estab
NEP-III Alaskan panhandle to N. of Puget Sound 1924 Def Estab
NEP-IV Puget Sound to Northern California 1947 Def Estab
P293 _CDA_P293 (Strait of Georgia) 1924 Def Unk
P297 _CDA_P297 (Strait of Georgia) 2006 Def Estab
NWP-4b None 0 Native Estab
P270 Willapa Bay 1947 Def Estab
NWP-4a None 0 Native Estab
EAS-III None 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Abbott, R. Tucker (1974) American Seashells, Van Nostrand Reinhold, New York. Pp. <missing location>

Academy of Natural Sciences of Philadelphia 2006-2014b OBIS Indo-Pacific Molluscan Database. <missing URL>

Carlton, James T. (1979) History, biogeography, and ecology of the introduced marine and estuarine invertebrates of the Pacific Coast of North America., Ph.D. dissertation, University of California, Davis. Pp. 1-904

Carlton, James T. (1992) Introduced marine and estuarine mollusks of North America: An end-of-the-20th-century perspective., Journal of Shellfish Research 11(2): 489-505

Coan, Eugene V.; Valentich-Scott, Paul; Bernard, Frank R. (2000) Bivalve Seashells of Western North Ameira, Santa Barbara Museum of Natural history, Santa Barbara CA. Pp. <missing location>

Cohen, Andrew N. and 22 authors (2001) <missing title>, Washington State Department of Natural Resources, Olympia. Pp. <missing location>

Eissinger, Ann (2009) <missing title>, Nahkeeta Northwest Wildlife Services, Bow WA. Pp. 1-26

Gillespie, Graham E. (2007) Distribution of non-indigenous intertidal species on the Pacific Coast of Canada, Nippon Suisan Gakkaishi 73(6): 1133-1137

Gillespie, Graham E.; Phillips, Antan C.; Paltzat, Debbie L.; Therriault, Tom W. 2007 Distribution of nonindigenous intertidal species on the Pacific Coast of Canada. <missing URL>

Hanna, G. Dallas (1966) Introduced mollusks of Western North America, Occasional Papers of the California Academy of Sciences 48: <missing location>

Huang, Zongguo (Ed.), Junda Lin (Translator) (2001) Marine Species and Their Distributions in China's Seas, Krieger, Malabar, FL. Pp. <missing location>

Ivanova, M. B.; Belogurova, L. S.; Tsurpalo, A. P. (2008) Ecological studies and the state of the ecosystem of Amursky Bay and the estuarine zone of the Razdolnaya River (Sea of Japan) Vol. 1., Dalnauka, Vladivostok, Russia. Pp. 1-140

Kil, Hyun Jong; Yoon, Sook Hee; Kim, Won; Choe, Byung Lae; Sohn, Hyun Joon; Park, Joong-Kee (2005) Faunistic investigation for marine mollusks in Jindo Island., Korean Journal of Systematic Zoology Special Issue 5: 29-46

Kolpakov, E. V. Kolpakov, N. V. (2013) [Local distribution and ecology of the rare bivalve mollusk Trapezium liratum (Trapezidae) in Peter the Great Bay (Sea of Japan)], Bulletin of the Russian Far East Malacological Society 17: 224-232

Kondo, Keiko Yamaguchi; Ueda, Shinji; Seike, Yasushi; Mitamura, Osamu (2009) Spatial distribution and growth of Trapezium liratum, an endangered species, in Lake Obuchi., Japanese Journal of Limnology 69(3): 237-245

Ruiz, Gregory M.; Geller, Jonathan (2018) Spatial and temporal analysis of marine invasions in California, Part II: Humboldt Bay, Marina del Re, Port Hueneme, and San Francisco Bay, Smithsonian Environmental Research Center & Moss Landing Laboratories, Edgewater MD, Moss Landing CA. Pp. <missing location>