Invasion History

First Non-native North American Tidal Record: 1832
First Non-native West Coast Tidal Record: 1871
First Non-native East/Gulf Coast Tidal Record: 1832

General Invasion History:

Myosotella myostis is native to the eastern Atlantic coastlines from the British Isles and western Baltic to the Mediterranean, where it inhabits the upper intertidal of salt marshes (Meyer 1955; Seelemann 1968; Bruydonycx et al. 2000). It has been introduced to the northwest Atlantic from Nova Scotia to the West Indies, the eastern Pacific from Washington to California, and the coasts of South America, South Africa, Australia, and New Zealand (Morrison 1963; Abbott 1974; Carlton 1979; Carlton 1992; Smith 1992; Martins 1996; Orensanz et al. 2002). Morrison (1963) noted that 'In my opinion this species has been introduced accidentally to every locality in which it is now living in the Western hemisphere. At least on the Atlantic coast of the United States, every such locality known to me is either a port or an oyster wharf. Because of the life history, which is known to include 'crawl away' young instead of a pelagic stage, Phytia (Myosotella) myostis still shows the same spotty distribution, many years after it first reached those places'. Likely vectors include dry ballast, cargo, and transplanted oysters. While this snail does not normally occur on oyster beds, transplanted oysters were often temporarily stored on shorelines or docks, where these snails are likely (Morrison 1963; Carlton 1992).

North American Invasion History:

Invasion History on the West Coast:

Myosotella myosotis was first recorded on the West Coast in San Francisco Bay in 1871 (Cooper 1872, cited by Carlton 1979). Given intense shell-collecting in the area, this snail was probably discovered soon after its introduction. It spread rapidly with shipping, and probably with oyster transplants, reaching Humboldt Bay by 1876, Los Angeles by 1915, and Puget Sound by 1936 (Carlton 1979; Carlton 1992). The current range on the West Coast is from Ojo de Liebre Lagoon (formally known as Scammon’s Lagoon), Mexico (Carlton 1979) to Nanaimo, Vancouver Island, British Columbia (Carlton 1979; Gillespie et al. 2007). This snail is found both in major port cities, but also in smaller ports where aquaculture, fishing, and recreational boating predominated. Myosotella myosotis is common under logs and other shore debris at the edge of marshes (Carlton 1979; Cohen and Carlton 1995; McLean 2007).

Invasion History on the East Coast:

On the East Coast, Myosotella myosotis was first reported from Narragansett Bay, Newport, Rhode Island as Melampus borealis by T. A. Conrad in 1832 (cited by Martins 1996). Gould (1841) described it (under the name Auricularia denticulata) as occurring in 'decaying wharves, about and below the high water mark', probably in the Boston Harbor and nearby ports. Stimpson (1851) in the 'Shells of New England' adds: 'It is perhaps an imported species'. By 1873, it was known to occur from Nova Scotia to Cape May, New Jersey (Gould 1870; Verrill and Smith 1873). It was collected in Chesapeake Bay in 1900 (Pilsbry 1900) and in Charleston, South Carolina in 1913 (Masyck 1913, cited by Harrison and Knott 2007). The southernmost record on the East Coast is from St. Augustine, Florida in 1997 (Florida Museum of Natural History 2013). The later appearance and scarcity of records in the south could represent the slower spread of the species or perhaps just less intense collecting.

Invasion History Elsewhere in the World:

Myosotella myostis has been widely transported around the world by shipping, often being described as a new species, producing a complex taxonomy with over 95 listed synonyms (Martins 1996). It has been introduced to Bermuda and Peru as Alexia bermudensis Adams 1855, South Africa as Alexia pulchella Morelet 1899, and South Australia as Auricula meridonalis Brazier 1877 (Martins 1996). This species was introduced to the southeast coast of South America by 1974 (Figueras and Sicardi 1974, cited by Orensanz et al. 2002). This snail does not appear to have become established in tropical regions.


Myosotella myosotis is a small, semi-terrestrial snail, occurring on the upper edges of salt-marshes and pilings. Its shell is ovate-fusiform and dextrally coiled with a pointed spire. It has 7-8 whorls, with a distinct suture and sometimes a spiral marginal line. The inner lip of adult shells has three white folds, with the lowest one formed by the lower lip. The outer lip has three inner teeth. The umbilicus is minute. The shell is dark-brown to purplish brown. Adult snails are 5-12 mm long. Considerable variability occurs in shape and color, even within populations (Bousfield 1960; Abbott 1974; Martins 1996).

This snail has a very complex taxonomy. Martins (1996) listed 97 synonyms. We have been selective, focusing primarily on names used in North American waters.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Gastropoda
Order:   Archaeopulmonata
Family:   Ellobiidae
Genus:   Myosotella
Species:   myosotis


Convulvulus myosotis (None, None)
Alexia bermudensis (H. & A. Adams, 1855)
Alexia myosotis (Pfieffer, 1854)
Alexia myostis marylandica (Pilsbry, 1900)
Alexia setifer (Cooper, 1872)
Auricularia myosotis (Draparnaud , 1801)
Carychium myosotis (None, None)
Carychium personatum (Micahud, 1831)
Melampus myostis (Jeffreys, 1869)
Ovatella myosotis (Meyer, 1955)
Phytia myosotis (Beck, 1837)
Voluta denticulata (Montagu, 1803)
Auricula myosotis (Draparnaud, 1801)
Melampus borealis (Conrad, 1832)
Auricula denticulata var. borealis (De Kay, 1843)

Potentially Misidentified Species

Detracia bulloides
Bubble Melampus: native from Florida and Bermuda, somewhat similar shell shape (Abbott 1974)



Myosotella myosotis is a small, air-breathing semi-terrestrial snail, occurring on the upper edges of salt-marshes and pilings. It is a simultaneous hermaphrodite. Individuals copulate, exchanging sperm and fertilizing their eggs (Barnes 1983; Ruthensteiner and Stocker 2009). The eggs are laid in masses on the substrate and develop directly into small snails. Egg development takes ~18 days at 20°C (Seelemann 1968). The snails hatch out at about 0.35 mm shell length and reach maturity at 5-10 mm in length (Martins 1996). Adults lay an average of ~550 eggs (Seelemann 1968).

Myosotella myosotis normally inhabits damp soil, wood, and vegetation above the waterline. Adults from the Mediterranean and Baltic survived 10-25 days underwater at salinities of 20-40 PSU (Seelemann 1968). Adults from the Baltic survived well for at least 6 weeks on a substrate moistened with freshwater, and at salinities as high as 50 PSU. Mediterranean animals survived substrate salinities as high as 90 PSU. Successful egg development for Baltic animals occurred at 5 to 40 PSU, while Mediterranean animals developed at 10-45 PSU. Optimum development for both populations was at ~10 PSU (Seelemann 1968). This snail feeds on bacteria, cyanobacteria, benthic diatoms, and epithelial cells of marsh plants (Seelemann 1968; Berman and Carlton 1991).


Detritius, benthic algae

Trophic Status:

Deposit Feeder



General HabitatCoarse Woody DebrisNone
General HabitatUnstructured BottomNone
General HabitatMarinas & DocksNone
General HabitatSalt-brackish marshNone
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Salinity RangeHyperhaline40+ PSU
Tidal RangeHigh IntertidalNone
Tidal RangeSupratidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Salinity (‰)0Adults of this airbreathing snail tolerate a substrate moistened with freshwater for up to 6 weeks (Seelemann 1968).
Maximum Salinity (‰)90Adults of Mediterranean populations tolerated substrate salinities up to 90 PSU. The upper limit for Baltic snails was 55 PSU (Seelemann 1968).
Minimum Reproductive Salinity5Normal egg development Baltic populations, 10 PSU for Mediterranean populations (Seelemann 1968).
Maximum Reproductive Salinity45Mediterranean populations, 40 PSU for Baltic populations. (Seelemann 1968).
Minimum Length (mm)5Minimum adult size (Seelemann 1968; Abbott 1974)
Maximum Length (mm)12Martins 1996
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNoneOligohaline-Hyperhaline

General Impacts

Only one study has been conducted comparing the biology or resource use of Myosotella myostis and native snails. In Coos Bay, Oregon, researchers found no evidence of competition between M. myostis and the native snails Assiminea californica (California Assiminea) and Littorina subrotundata (Salt Marsh Periwinkle). However, the M. myostis population is concentrated in higher levels of the marsh, while the native species are more abundant in the lower marsh (Berman and Carlton 1991).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
MED-II None 0 Native Estab
MED-III None 0 Native Estab
MED-IV None 0 Native Estab
MED-VII None 0 Native Estab
MED-V None 0 Native Estab
MED-VI None 0 Native Estab
MED-IX None 0 Native Estab
NEA-II None 0 Native Estab
NEA-III None 0 Native Estab
NA-ET2 Bay of Fundy to Cape Cod 1841 Def Estab
NA-ET1 Gulf of St. Lawrence to Bay of Fundy 1960 Def Estab
NA-ET3 Cape Cod to Cape Hatteras 1832 Def Estab
CAR-VII Cape Hatteras to Mid-East Florida 1913 Def Estab
NA-ET4 Bermuda 1855 Def Estab
NEP-V Northern California to Mid Channel Islands 1871 Def Estab
NEP-VI Pt. Conception to Southern Baja California 1915 Def Estab
NEP-IV Puget Sound to Northern California 1876 Def Estab
NEP-III Alaskan panhandle to N. of Puget Sound 1936 Def Estab
SA-II None 1974 Def Estab
NZ-IV None 1980 Def Estab
NEA-V None 0 Native Estab
SEP-C None 1837 Def Estab
NEA-VI None 1860 Crypto Estab
NEA-IV None 0 Native Estab
WA-I None 1878 Crypto Estab
AUS-VII None 1877 Def Estab
WA-V None 1889 Def Estab
AUS-VIII None 1992 Def Estab
AUS-X None 1992 Def Estab
M060 Hudson River/Raritan Bay 1865 Def Estab
P050 San Pedro Bay 1915 Def Estab
P130 Humboldt Bay 1876 Def Estab
P170 Coos Bay 1965 Def Estab
M130 Chesapeake Bay 1900 Def Estab
M040 Long Island Sound 1869 Def Estab
M010 Buzzards Bay 1913 Def Estab
M020 Narragansett Bay 1832 Def Estab
S183 _CDA_S183 (Daytona-St. Augustine) 1997 Def Estab
P040 Newport Bay 1925 Def Estab
P070 Morro Bay 1972 Def Estab
P080 Monterey Bay 1945 Def Estab
P090 San Francisco Bay 1871 Def Estab
P095 _CDA_P095 (Tomales-Drakes Bay) 1975 Def Estab
P110 Tomales Bay 1946 Def Estab
P112 _CDA_P112 (Bodega Bay) 1944 Def Estab
P290 Puget Sound 1936 Def Estab
P200 Alsea River 1978 Def Estab
P210 Yaquina Bay 1978 Def Estab
P270 Willapa Bay 1963 Def Estab
P280 Grays Harbor 1965 Def Estab
P297 _CDA_P297 (Strait of Georgia) 1963 Def Estab
P286 _CDA_P286 (Crescent-Hoko) 1945 Def Estab
P292 _CDA_P292 (San Juan Islands) 1998 Def Estab
P293 _CDA_P293 (Strait of Georgia) 1961 Def Estab
CAR-II None 1996 Def Unk
S130 Ossabaw Sound 1996 Def Estab
S030 Bogue Sound 1996 Def Estab
M128 _CDA_M128 (Eastern Lower Delmarva) 1972 Def Estab
M120 Chincoteague Bay 1972 Def Estab
M090 Delaware Bay 1873 Def Estab
N170 Massachusetts Bay 1841 Def Estab
N130 Great Bay 1996 Def Estab
N100 Casco Bay 1996 Def Estab
N010 Passamaquoddy Bay 1873 Def Estab
S080 Charleston Harbor 1913 Def Estab
N195 _CDA_N195 (Cape Cod) 1873 Def Estab
P093 _CDA_P093 (San Pablo Bay) 1871 Def Estab
N050 Penobscot Bay 1996 Def Estab
B-III None 0 Native Estab
CAR-IV None 1979 Def Unk
P240 Tillamook Bay 1976 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
26572 Carlton 1979; Cohen and Carlton, 1995 1876 1876-01-01 Eureka Def 40.7864 -124.1922
26784 Cohen, et al. 2005 (SF Bay Area RAS) 2004 2004-05-27 Petes Harbor, San Francisco Bay Def 37.5006 -122.2242
28980 Wasson et al, 2001 (Elkhorn Slough Survey) 1998 1998-03-01 Elkhorn Slough Station 2 Def 36.8019 -121.7854
29759 Carlton 1979; Cohen and Carlton, 1995 1944 1944-01-01 Bodega Harbor Def 38.3262 -123.0495
30035 Cohen, et al. 2005 (SF Bay Area RAS) 2004 2004-05-28 Moores Landing, San Francisco Bay Def 38.2261 -122.3076
30060 Carlton 1979); Cohen and Carlton 1995 1915 1915-01-01 Los Angeles/Long Beach Harbor Complex Def 33.7632 -118.2526
30160 Carlton 1979; Cohen and Carlton, 1995 1925 1925-01-01 Newport Bay Def 33.6092 -117.9067
30387 Carlton 1979; Cohen and Carlton, 1995 1945 1945-01-01 Elkhorn Slough General Location Def 36.8086 -121.7856
30517 Cohen and Carlton, 1995 1871 1871-01-01 San Francisco Bay Def 37.8494 -122.3681
31231 Carlton 1979; Cohen and Carlton, 1995 1920 1920-01-01 Bolinas Lagoon Def 37.9189 -122.6816
31353 Cohen and Carlton, 1995 1964 1964-01-01 Anaheim Bay Def 33.7333 -118.0894
31551 Cohen, et al. 2005 (SF Bay Area RAS) 2004 2004-05-24 San Leandro Marina, San Francisco Bay Def 37.6966 -122.1932
33701 Cohen and Carlton, 1995 1946 1946-01-01 Tomales Bay Def 38.2100 -122.9400
33982 Carlton 1979; Cohen and Carlton, 1995 1972 1972-01-01 Morro Bay Def 35.3500 -120.8500


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