This post is based on work done to produce Virginia Water Radio Episode 262 (4/20/15), a 3 min./28 sec. podcast on this topic, available online at http://www.virginiawaterradio.org/2015/04/episode-262-4-20-15-freshwater-snails.html. Have a listen!
All Internet addresses mentioned were functional as of 4/22/15.
What group of animals has an infamous reputation for moving slowly, leaving a slimy trail, and living in a shell?
That would, of course, be snails.
Snails, which along with slugs are called gastropods, make up one class of the animals known as mollusks, referred to by scientists as Phylum Mollusca. The mollusks phylum, comprising well over 100,000 species, also includes two-shelled animals (known as bivalves), such as clams, mussels, and oysters; squids and octopuses, which have an internal shell; and several other groups. But a large majority of mollusks are gastropods, particularly snails.
Most snails are either land-based, or terrestrial, or live in marine waters. But many species of freshwater snail species also exist, including several hundred in North America. About 70 native or naturalized snail species live in Virginia’s streams, rivers, ponds, lakes, and other freshwater bodies (compared to over 150 snail species that live on land in Virginia). And Virginia’s streams in the Ohio River basin are part of one of North America’s most species-rich freshwater snail areas.
Like most land snails, most aquatic snails have a single shell, which differs in shape and size among different snail families. Most freshwater species have a coiled and spiral shell, but some species have flat coiled shells, and some have flat, non-coiled shells.
As noted above, snails are called gastropods, a word whose roots mean “stomach” and “foot.” This is because part of snails’ digestive system is in their fleshy foot, which snails use to attach to rocks, plants, or other surfaces and to move along a slimy trial of mucus secreted by the foot.
Snails play important roles in food webs and in the cycling of energy and nutrients in aquatic ecosystems. Most freshwater snails feed by scraping algae off the surface to which the snail’s attached; this algae grazing can help regulate and invigorate the algal community, which is one main source of food and energy in aquatic systems. Removing algae from underwater plants can also help those plants get the light they need (just as algae need) to conduct photosynthesis. Freshwater snails, in turn, are food for a large number of other animals, including certain fish, amphibians, waterfowl, and turtles.
Snails might have reputation for being slow, slimy, and shell-bound, but a remarkable number of things living under fresh water are influenced by these diverse and widespread mollusks.
Freshwater snails in the South Fork Roanoke River near Elliston, Va. (Montgomery County), July 13, 2014.
Below are sources of more information to help you learn more about freshwater snails and mollusks generally. Following the sources is information on how this post may help Virginia’s teachers with various science Standards of Learning.
Sources for this Post and for More Information
Illinois Natural History Survey, “Mollusks,” online at http://wwx.inhs.illinois.edu/outreach/animals/mollusks/.
T. Dillon, Jr., et al., “The Freshwater Gastropods of North America,” online at http://www.fwgna.org/. This is an effort to document the species in all 15 families of gastropods in North America north of Mexico. The Virginia section of the Web site is at http://www.fwgna.org/FWGVA/.
ETI Bioinformatics/Key to Nature Series, online at http://www.keytonature.eu/wiki/ETI_BioInformatics. The “Marine Species Identification Portal/Molluscs” is available online at http://species-identification.org/index.php?groep=Molluscs&selectie=12&hoofdgroepen_pad=%2C1%2C12. The site identifies the many species of gastropods and other mollusks (also written “molluscs”) that inhabit marine waters worldwide.
Paul D. Johnson, Freshwater Snail Biodiversity and Conservation, Pub. No. 420-630, Virginia Cooperative Extension, Blacksburg, Va., 2009; available online at https://pubs.ext.vt.edu/420/420-530/420-530_pdf.pdf.
New Hampshire Public Television’s Nature Works Web site, “Squid and Octopus,” online at http://www.nhptv.org/natureworks/nwep6f.htm.
Virginia Department of Game and Inland Fisheries (VDGIF), “Fish and Wildlife Information Service,” online at http://vafwis.org/fwis/?Menu=Home.Species+Information. “Snails” search results on 4/15/15 at this link (234 species). One can search by common name or scientific name of species or groups.
VDGIF, “Freshwater Mussels,” online at http://www.dgif.virginia.gov/wildlife/freshwater-mussels.asp; and “Freshwater Mussel Restoration,” http://www.dgif.virginia.gov/awcc/freshwater-mussel-restoration/.
VDGIF, “List of Native and Naturalized Fauna of Virginia—March 2012,” available online at http://www.dgif.virginia.gov/wildlife/virginianativenaturalizedspecies.pdf (lists freshwater and [in part] terrestrial snails, but not marine species).
Reese Voshell, Jr., A Guide to Common Freshwater Invertebrates of North America, McDonald & Woodward, Blacksburg, Va., 2002.
SOLs Information for Virginia Teachers
This episode may help with the following Virginia’s 2010 Science Standards of Learning (SOLs).
Earth Resources: 4.9 (Virginia natural resources);
Life Processes: 1.5 (basic needs), 3.4 (adaptations);
Living Systems: 3.5 (food chains), 3.6 (aquatic ecosystems), 4.5 (ecological interactions), 5.5 (organism features and classification), 6.7 (watersheds: snail diversity in Ohio River basin).
LS.4 (features and classification);
LS.6 (ecosystem components and cycles);
LS.8 (population interactions);
LS.9 (adaptations for particular ecosystems).
BIO.8 (interactions among populations, communities, and ecosystems; including analysis of the flora, fauna, and microorganisms of Virginia ecosystems).
Virginia’s SOLs are available from the Virginia Department of Education, online at http://www.doe.virginia.gov/testing/.