Invasion History

First Non-native North American Tidal Record: 2005
First Non-native West Coast Tidal Record: 2005
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Littoridinops monroensis is native to estuarine waters from Maryland to Florida, Alabama (and possibly Texas), and the Bahamas (Thompson 1999; Hershler et al. 2007; Academy of Natural Sciences of Philadelphia 2013; Rosenberg 2013). It occurs in fresh waters of the Florida peninsula (Thompson 1999) and was recently (2009) discovered in coastal lagoons of southwestern Cuba, a range extension which Vazquez et al. (2010) attributed to migratory birds.

North American Invasion History:

Invasion History on the West Coast:

Littoridinops monroensis was discovered in 2005 in tidal marshes of Suisun Bay, California in the San Francisco Delta region and in marshes of San Pablo Bay, about 30 km west (seaward), at salinities of 2-17 PSU. The snails were very abundant, over a 3-year period and appear to be well-established. This snail lacks a planktonic larval stage, but could be transported in ballast water sediments (Hershler et al. 2007). An earlier introduction in dry ballast or an introduction from freshwater populations in Florida, with ornamental aquatic plants, is also possible.


Littoridinops monroensis is a very small estuarine snail. Its shell is conical and dextrally coiled, with a sharp, pointed apex, consisting of 5-6 whorls. The whorls are slightly convex with shallow sutures. The aperture is about 1/2 the shell height, ovate to sub-circular, and sharply angled above. The inner lip is moderately thick, while the outer lip is a 'slight glaze'. The shell has a narrow umbilicus. The periostracum is tan or brown, but with spirals in juvenile snails. Maximum size is around 5.5 mm. Female shells from the upper San Francisco Bay ranged from 3.6 to 4.3 mm. Males are smaller, reaching a maximum of 2.8 mm, and have a prominent penis which is about 0.5 mm in length (Hershler et al. 2007). The penis has 17-50 papillae along its right margin arranged in 3-5 rows (Thompson 2004). Hydrobiid snails, as a group, require identification by specialists, and are not adequately covered in general guidebooks (e.g. Abbott 1974; Morris 1975; Gosner 1978; McLean 2007).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Gastropoda
Order:   Neotaenioglossa
Family:   Cochliopidae
Species:   monroensis


Hydrobia monroensis (Frauenfield, 1883)
Amnicola forsythi (Pilsbry, 1930)

Potentially Misidentified Species

Littoridinops palustris
Native from Florida to Maryland

Littoridinops tenuipes
Native to the Gulf Coast of Florida and Alabama

Potamopyrgus antipodarum
Commonly known as the New Zealand Mudsnail, widely introduced in coastal fresh-brackish waters in Western North America, and in portions of the Great Lakes.

Tryonia imitator
Native to California estuaries

Tryonia porrecta
Native to mineralized springs of the interior West, cryptogenic in brackish marshes of the San Francisco estuary (Hershler et al. 2007)



Littoridinops monroensis is a small estuarine snail, occurring in brackish tidal marshes and lagoons, and also in non-tidal fresh waters in Florida (Thompson 2004; Hershler et al. 2007). Sexes are separate and eggs are fertilized by copulation. Development is direct, without a planktonic larva (Hershler et al. 2007).

Littoridinops monroensis ranges from temperate climates (e.g. Maryland) to subtropical climates (e.g. Florida, Bahamas, Cuba) including interior freshwaters and estuaries from 1 to 31 PSU (Thompson 2004; Hershler et al. 2007; Vazquez et al. 2012). Hydrobiid snails, such as L. monroensis, feed on organic deposits, benthic diatoms, and can also scrape microbes off sand particles (Lopez and Kofoed 1980).


Detritus, microalgae

Trophic Status:

Deposit Feeder



General HabitatFresh (nontidal) MarshNone
General HabitatGrass BedNone
General HabitatNontidal FreshwaterNone
General HabitatTidal Fresh MarshNone
General HabitatSalt-brackish marshNone
General HabitatUnstructured BottomNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEndobenthicNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Salinity (‰)0This species occurs in freshwater (Thompson 1999; Hershler et al. 2007)
Maximum Salinity (‰)31Filed, Vázquez et al. 2012)
Maximum Length (mm)4.3Females. Males have a maximum size of 3.6 (Hershler et al. 2007).
Broad Temperature RangeNoneWarm temperate-Subtropical
Broad Salinity RangeNoneTidal Limnetic-Polyhaline

General Impacts

Littoridinops monroensis is abundant in some marshes in the San Francisco Bay, but no impacts are reported.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 0 Native Estab
CAR-VII Cape Hatteras to Mid-East Florida 0 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 0 Native Estab
NEP-V Northern California to Mid Channel Islands 2005 Def Estab
P090 San Francisco Bay 2005 Def Estab
P093 _CDA_P093 (San Pablo Bay) 2005 Def Estab
CAR-II None 2009 Crypto Estab
CAR-V None 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
31597 Foss 2009 2005 2005-10-07 New York Point Marina Def 38.0400 -121.8863
33483 Hershler et al. 2007 2005 2005-01-01 Contra Costa County Def 38.0360 -122.0710


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

Academy of Natural Sciences of Philadelphia 2002-2016a Malacology Collection Search.

Foss, Stephen (2009) <missing title>, California Department of Fish and Game, Sacramento CA. Pp. <missing location>

Gosner, Kenneth L. (1978) A field guide to the Atlantic seashore., In: (Eds.) . , Boston. Pp. <missing location>

Hershler, Robert; Davis, Cheryl L.; Kitting, Christopher L.; Liu, Hsiu-ping (2007) Discovery of introduced and cryptogenic cochliopid gastropods in the San Francisco estuary, California., Journal of Molluscan Studies 73: 323-332

Lopez, G. R.; Kofoed, L. H. (1980) Epipsammic browsing and deposit feeding in mud snails Hydrobiidae., Journal of Marine Research 38(4): 585-600

McLean, James A. (2007) The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon, University of California Press, Berkeley CA. Pp. 713-1766

Morris, Percy A. (1975) A field guide to shells of the Atlantic, Houghton-Mifflin, Boston. Pp. <missing location>

Rosenberg, Gary 1995-2015 Malacolog.

Thompson, Fred G. 2004 An identification manual for the freshwater snails of Florida an identification manual for the freshwater snails of florida an identification manual for the freshwater snails of florida an identification guide for the freshwater sn.

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database. <missing description>

Vázquez, Antonio A.; Cobian, Dorka; Sánchez, Jorge; Pointier, Jean-Pierre (2012) First record of Littoridinops monroensis (Frauenfeld, 1863) (Gastropoda: Cochliopidae) in Cuba through a likely natural dispersal event, Molluscan Research Molluscan Research 32(1): 50-54