Invasion History

First Non-native North American Tidal Record: 2007
First Non-native West Coast Tidal Record: 2007
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Assiminea parasitologica is a small snail, native to southern Japan and the southern coast of Korea (Kuroda et al. 2003; James T. Carlton, personal communication 2007). It is introduced in Oregon, where it was first found in 2007 in Coos Bay. It was subsequently found in other Oregon estuaries, including the Yaquina, Alsea, Umpqua and Coquille (Laferriere et al. 2010; Davidson 2013). This snail has a planktonic larva, and has the potential to be dispersed in ballast water. Since this snail can tolerate some air exposure, transport on the deck or the above-water hulls of ships is possible.

North American Invasion History:

Invasion History on the West Coast:

A small, unidentified snail was discovered July 5, 2007 in an upper estuary slough (10 PSU) of Coos Bay, Oregon at densities of thousands meter-2 (Carlton personal communication 2007; Laferriere et al. 2010). It was identified by Robert Hershler of the US National Museum of Natural History. It was subsequently found in the Umpqua and Yaquina Rivers in 2008 and the Alsea and Coquille Estuaries in 2009 (Laferriere et al. 2010; South Slough National Estuarine Research Reserve 2013).


Assiminea parasitologica is a small snail, about 5 mm in height. It is dextrally coiled, with 4-5 bulbous whorls in its rounded, bluntly conical shell. The youngest whorl is about 2/3 of the shell length. Its aperture has a broad inner lip. The overall color is brown, with some reddish tints. Younger shells have light yellow bands at the top and bottom of the body whorl, which become eroded as the animal matures. It inhabits the upper intertidal regions of salt and brackish marshes. The larvae of this snail are planktonic, but have not yet been described. Description from: Kuroda 1958; James T. Carlton, personal communication 2007; Laferriere et al. 2010; Davidson 2013.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Gastropoda
Order:   Neotaenioglossa
Family:   Assimineidae
Genus:   Assiminea
Species:   parasitologica


Potentially Misidentified Species

Assiminea californica
Native species with five whorls, more conical and 2-3.5 mm in size. Ranges from British Columbia-Mexico and is found in upper intertidal marshes.

Littorina subrotundata
Native with four well-rounded whorls, a thin outer lip, and 5-7 mm in size. Ranges from British Columbia to Northern California and is found in salt marsh edges. 

Potomopyrgus antipodarum
Introduced New Zealand Mudsnail, has 7-8 whorls and is 5-12 mm in size.  It is found on mud in fresh and brackish water from California to British Columbia.



Assiminea parasitologica is a small snail inhabiting upper regions of tidal marshes (Kuroda et al. 2003; Laferriere et al. 2010). Snails of the genus have separate sexes and vary in their modes of reproduction. Some, such as A. californica, and the East Coast A. succinea, lay egg capsules and have direct development (J. P E. Morrison, cited by Wass 1972; Fowler 1980). This snail has planktonic development, but descriptions of larvae have not been published. In the Coos River estuary, Oregon, mating occurred in June-July, with young-of-the year appearing in August (Laferriere et al. 2010).

Assiminea parasitologica inhabits the middle-to-upper reaches of estuarine tidal marshes in its native Japan (Kuroda et al. 2003) and introduced range in Oregon (Laferriere et al. 2010). It tolerates a wide range of temperatures and salinities, although specific data on its tolerances are not available. In the Coos River estuary, it ranges from oligohaline (0-5 PSU) to euhaline (30-35 PSU) zones, but is most abundant in the mesohaline regions (5-18 PSU) (Laferriere et al. 2010). Snails of these genus tolerate considerable air exposure, but occur on moist, vegetated substrates (Fowler 1980; Kuroda et al. 2003). They probaly feed on plant detritus and benthic microalgae. This snail is vulnerable to predators such as crabs and shorebirds. It is of particular interest as the first host of a lung fluke, Paragonimus ohirae, whose second hosts are grapsid crabs, and ultimately infect rats and weasels (Agatsuma and Habe 1986).


Detritus, benthic microalgae


Shorebirds, crabs

Trophic Status:

Deposit Feeder



General HabitatSalt-brackish marshNone
General HabitatUnstructured BottomNone
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeMid IntertidalNone
Tidal RangeHigh IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Broad Temperature RangeNoneWarm temperate
Broad Salinity RangeNoneOligohaline-Euhaline

General Impacts

Ecological impacts of Assiminea parasitologica have not yet been observed in Oregon. Potential concerns are the possibility of competition with native marsh fauna and the possible introduction of parasites that could affect native wildlife.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-IV Puget Sound to Northern California 2007 Def Estab
P170 Coos Bay 2007 Def Estab
NWP-3a None 0 Native Estab
P180 Umpqua River 2008 Def Estab
P210 Yaquina Bay 2008 Def Estab
P160 Coquille River 2009 Def Estab
P200 Alsea River 2009 Def Estab
NWP-4a None 1958 Native Estab
NWP-3b None 0 Native Estab
NWP-5 None 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Agatsuma, Takeshi; Habe, Shigehisa (1986) Genetic variability and differentiation of natural populations in three Japanese lung flukes, Paragonimus ohirai, Paragonimus iloktsuenensis and Paragonimus sadoensis (Digenea:Troglotrematidae), Journal of Parasitology 72(3): 417-433

Davidson, Timothy M. 2013 <i>Assiminea parasitologica</i> - Asian marsh snail. <missing URL>

Fowler, Bruce H. (1980) Reproductive biology of Assiminea californica (Tryon , 1865), The Veliger 23(9): 2

Fretter, Vera; Graham, Alastair (1962) British prosobranch molluscs: their functional anatomy and ecology, In: (Eds.) . , London. Pp. <missing location>

Kuroda, Miki ; Wada, Keiji; Kamada, Mahito; et al. (2003) [Distribution patterns of assimineid species (Gastropoda: Rissooidea) in the salt marshes of the Yoshino River, Tokushima Prefecture, Japan], Yuriyagai 9(1): 21-31

Kuroda, Tokube (1958) On the more species of Assiminea from Japan, Venus 33: 16-22

Laferriere, Alix M.; Harris, Heidi; Schaefer, John (2010) <missing title>, South Slough National Estuarine Research Reserve and Confederated Tribes, Coos Bay OR. Pp. 1-163

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>

South Slough National Estuarine Research Reserve 2013 <i>Spartina alterniflora</i> (smooth cordgrass) in the Coos Estuary. <missing URL>

USGS Nonindigenous Aquatic Species Program 2003-2024 Nonindigenous Aquatic Species Database.

Wass, Melvin L. (1972) A Checklist of the Biota of Lower Chesapeake Bay, None <missing volume>: <missing location>