> Lymnaea (Fossaria) humilis Say 1822

> Habitat & Distribution
Lymnaea humilis populations are widely distributed from the tree line in Alaska and Canada to Arizona and Florida (Burch 1989, Jokinen 1992). The snail is frequently semiaquatic, inhabiting moist areas at or above the water line near streams, lakes, ponds, and marshes (Clarke 1981, Stewart and Dillon 2004). Lymnaea humilis can inhabit oligotrophic, mesotrophic, or eutrophic water bodies (Clarke 1979) and is an excellent colonizer of new habitats, readily invading young ponds devoid of vegetation and other species of gastropods (Jokinen 2005).

The species is moderately widespread in the northern and central regions of North Carolina, but becomes less common in the south.  For quite a few years I was unable to locate any populations of L. humilis in South Carolina whatsoever, especially puzzling in view of the fact that its type locality was given as "South Carolina" by Say (1822).  Recently, however, our good colleague Bryan England has discovered a population of L. humilis in a marshy area along the Catawba River in Lancaster County, SC.  We also have one record from Georgia, in the Yellow River at Porterdale.

> Ecology & Life history
Although L. humilis can thrive in waters with low levels of dissolved oxygen, populations in Manitoba disappeared from several sites affected by intensive agriculture and logging (Pip 2000). Flooding from hydro dams has also caused local extinctions of semiaquatic L. humilis populations in Manitoba.

Like other pulmonate snails, L. humilis is monecious and almost certainly capable of self-fertilization as well as outcrossing (Dillon 2000). Egg masses are gelatinous, transparent, and sausage-shaped (Clarke 1981). Studies of population size frequency distribution have suggested an annual life cycle (Type A of Dillon 2000: 156 - 162), with a maximum lifespan of 16 months (McKillop 1985, Jokinen 1992). One breeding study revealed that L. humilis breeds continuously throughout the summer (Brown 2001). 

Lymnaea humilis is one of many amphibious lymnaeid taxa capable of serving as an intermediate host for trematodes causing fascioliasis in livestock, and rarely humans (Remigio 2002, Mas-Coma et al. 2005).

> Taxonomy & Systematics
Burch (1989) gathered humilis together with ten other nominal species and subspecies of small, amphibious lymnaeids and placed them in the genus Fossaria (Westerlund 1885), subgenus Fossaria (s.s.). We prefer Hubendick’s (1951) two-genus classification of the Lymnaeidae, however, Fossaria being at most a subgenus.  We agree with Hubendick that most of the ten nomina in Burch’s subgenus Fossaria(s.s.) will prove to be junior synonyms of humilis, including cyclostoma, dalli, exigua, galbana, modicella, obrussa, parva, peninsulae, rustica, and tazewelliana. Alternate generic names under which these species have been listed include Galba, Limnaea, and Limnophysa as well as Fossaria.

> Essay #1
See my 28Dec06 post to the FWGNA group reviewing the classification of the Lymnaeidae.

> Essay #2
The taxonomy of Lymnaea humilis has become elaborately entangled with that of L. cubensis.  See my 25June08 essay on the type locality of L. humilis for more.  There's also a link to a nice photo of the radula.

> Interesting Photo
Blackbeard's Lymnaea humilis, courtesy of Aydin Orstan.

> Maps of Lymnaea distribution
Click the small map to enlarge it, or download the state-specific PDF



North Carolina (PDF)

> References
Brown, K.M. 1982. Resource overlap and competition in pond snails: an experimental analysis. Ecology 63:412-422. Brown, K.M. 2001. Mollusca: Gastropoda. In: J.H. Thorp and A.P. Covich, eds., Ecology and Classification of North American Freshwater Invertebrates, Academic Press, New York. Pp. 297-329. Burch, J.B. 1989. North American Freshwater Snails. Malacological Publications, Hamburg, Michigan. Clarke, A.H. 1979. Gastropods as indicators of trophic lake stages. Nautilus 93:138-142. Clarke, A.H. 1981. The Freshwater Molluscs of Canada. National Museum of Natural Sciences, National Museums of Canada, Ottawa, Canada. Dillon, R.T., Jr. 2000. The Ecology of Freshwater Molluscs. Cambridge University Press, Cambridge, United Kingdom. Hubendick, B. 1951. Recent Lymnaeidae. Their variation, morphology, taxonomy, nomenclature, and distribution. Kungl. Svenska Vetensk. Akad. Handl., 3, 1-223. Jokinen, E.H. 1992. The Freshwater Snails (Mollusca: Gastropoda) of New York State. NY State Mus Bull 482, Albany, New York. Jokinen, E.H. 2005. Pond molluscs of Indiana Dunes National Lakeshore: then and now. Amer Malac Bull 20:1-9.  Mas-Coma, S., M. D. Bargues, & M. A. Valero  2005.  Fascioliasis and other plant-borne trematode zoonoses.  Int. J. Parasit. 35: 1255-1278.  McKillop, W.B. 1985. Distribution of aquatic gastropods across the Ordovician dolomite – Precambrian granite contact in southeastern Manitoba, Canada. Can J Zool 63:278-288. Pip, E. 2000. The decline of freshwater molluscs in southern Manitoba. Can Field-Nat 114:555-560.   Remigio, E. A.  2002.  Molecular phylogenetic relationships in the aquatic snail genus Lymnaea, the intermediate host of the causative agent of fascioliasis: insights from broader taxon sampling.  Parasitology Reserach 88: 687-696.  Stewart, T.W., and R.T. Dillon, Jr. 2004. Species composition and geographic distribution of Virginia’s freshwater gastropod fauna: a review using historical records. Amer Malac Bull 19:79-91.