Daily Invader

Chesapeake Bay Snails and Sea Slugs

Atlantic Assiminea (Assiminea succinea)


Atlantic Assiminea (Assiminea succinea) is a tiny snail, could it have been overlooked? Photo by Stan Boul.






Atlantic Assiminea is a tiny (2.5 mm) salt marsh snail found along the Atlantic coast from Brazil to Massachusetts. Because this species is so tiny it is easily overlooked and the original range is uncertain. It was first seem in Brooklyn, NY in the mid 1800s suggesting that it could be native to the Mid-Atlantic region, however, it wasn’t seen in the Chesapeake Bay until 1935 and its frequent association with docks and ports suggesting that it may be introduced. Since we can’t say for sure if it’s native or introduced we consider it cryptogenic in Chesapeake Bay and other estuaries north of Cape Hatteras. Other snails of similar size and habit (Ovatella myosotis) were collected in the bay in the early as 1900s but Atlantic Assiminea is not very common and could have been overlooked. Atlantic Assiminea was first seen on Smith's Island and Fisherman's Island in NorthHampton County VA in 1935 and Shell Bay, Chincoteague Bay, and several others in the area in 1950. In 1952 it was collected in the Potomac River and from the Rappahannock in 1972. JPE Morrison, Smithsonian malacologist, attributed its appearance in the Bay to the oyster shell trade in which oyster shell from the Carolinas was planted in the Bay to encourage oyster spatfall. Complete Record 


Chinese and Japanese Mystery Snails (Bellamya chinensis, B. japonica)


Chinese and Japanese Mystery Snails (Bellamya chinensis, B. japonica) get their common name because of the sudden appearance of their young.







What’s so mysterious about mystery snails? Mystery snails are the largest freshwater snails in the region (max 3 inches). They have spiral shells with a door (operculum) used to seal themselves inside. Unlike most freshwater snails, they give birth to live young. The sudden appearance of baby snails surprised aquarists, hence the name mystery snails. The identification of these snails has been confused many times and there was debate about whether or not Japanese Mystery Snails (Bellamya japonica) and Chinese Mystery Snails (Bellamya chinensis) are actually the same species. A recent study shows that they are different species, but here they are lumped together. Mystery snails are native to Asia where they are a common food item. In 1892 they were imported to Chinese markets in San Francisco and by 1911 had established around San Jose and San Francisco. Over time the snails moved from the Chinese food markets into the aquarium trade and were transported across the country for use in aquarium and ornamental ponds. They are now widespread in ponds, lakes, and reservoirs from California to British Columbia and Florida to Quebec. The first reports of the snails in the Chesapeake region were in the 1960s when they were found in the Susquehanna and Potomac Rivers. They are now common in the Potomac and Susquehanna, but elsewhere in Chesapeake their abundance and distribution is unknown. Their shells are large and conspicuous, so let us know if you find them in a new river. Complete Record 


Faucet Snail (Bithynia tentaculata)


Faucet Snail (Bithynia tentaculata) are a big problem for the ducks that eat them.  



Faucet Snails are small (15mm) freshwater snails native to Europe. They were first reported in Lake Michigan in 1871, where they may have been transported with dry ballast, aquatic plants, or material used for packing fragile goods. From there they spread into all the other Great Lakes, the Hudson River, and reached the Potomac River in the 1920s. They were collected in the tidal Potomac River near Alexandria, VA in 1927 and have spread through much of the Potomac basin, becoming one of the most abundant snails by the 1970s. More recently, in 2004, they were found in the Big Gunpowder Falls and Patapsco Rivers in Baltimore County, MD. The full extent of this snail’s range in the Bay watershed is not known, but where present, they may complete with native freshwater snails. In Quebec and Wisconsin, they have been linked to extensive deaths of wild ducks caused by trematodes (flatworm parasites), which spend part of their life cycle in the snail. Complete Record 


Lake Merritt Cuthona (Cuthona perca)


Lake Merritt Cuthona (Cuthona perca) is a sea slug that really gets around.





Lake Merritt Cuthona is a sea slug (nudibranch). Sea slugs in the same group as snails (gastropod mollusks) but they don’t have shells and all are aquatic. They have gills that often look like lobes along their sides and backs. Because some species are brilliantly colored, or interestingly shaped, self-taught divers have often played a big role in tracking their distribution and biology. Lake Merritt Cuthona is translucent white with opaque white and olive flecks. Some considered them native to the tropical Western Atlantic, but its present far-flung range calls that assumption into question. They were first collected and described in Brazil in the 1950s but are widely distributed. They have been found in the Caribbean, Jamaica, Colombia, Barbados, Florida, Ghana, the Mediterranean, San Francisco Bay, Hawaii, and New Zealand, just to name a few. In the Chesapeake, they were collected in Norfolk Harbor in 1994 and 1995 and several other locations in the lower Bay indicating that they have become established. Their arrival in the Bay is fairly recent and there are indications that they were introduced in ballast water or through hull fouling. This nudibranch feeds on hydroids and sea anemones, including the introduced Striped Sea Anemone (Diadumene lineata). Complete Record 


Common Periwinkle (Littorina littorea)


Common Periwinkle (Littorina littorea) are snails with a long and complicated history in the US and Canada.



Common Periwinkles small snails that like on rocky shores. They are native to Europe from the White Sea to Gibraltar. The status of these snails as native or introduced in North America has been debated for a long time, but recent molecular analysis strongly supports an introduced status for these snails. This study found that evidence of multiple introductions, possibly as early as Viking times, as well as in the 1800 and 1900s. Some very old specimens have been found in Nova Scotia and Newfoundland in Indian and Norse archaeological sites dating back to ~1000-1300 B.C. Early Viking explorers used these snails as food and may have introduced them. For the Chesapeake Bay region the evidence for introduction is clearer. The first reports from the Atlantic Coastal Bays were from specimens collected on a jetty at West Ocean City in 1959. They were also found at Assateague Island and Chincoteague in the 1970s and late 1980s. Common Periwinkles are still rare in the Chesapeake region and probably have had no impact on native biota. However, this species has had a dramatic ecological impact on the biota of the northern Atlantic coast of North America. Complete Record


Salt Marsh Snail Myosotella myosotis


Once introduced, the salt marsh snail Myosotella myosotis tends to stay put.


Myosotella myosotis is a small brown salt marsh snail, native to Europe (British Isles, Mediterranean, etc.), that is sometimes called the mouse-ear marsh snail. It has been introduced into several locations including the East Coast of North America from Nova Scotia to the West Indies, the US west coast from Washington to California, South Africa, Australia, and New Zealand. Introduction of this snail could have occurred by several means including, dry ballast (rocks and dirt used for weight on old sailing vessels), the oyster trade, and discarded packing material. Once these snails have been introduced to a new location thier local range expansion is limited, thus their distribution remains spotty for years after introduction. These snails were first reported in Chesapeake Bay in 1900 in St. Leonard’s Creek, a Patuxent River tributary. But over the years they have shown up in several other locations including Fisherman's Island (Northampton Co), VA, at the mouth of the Bay, Norfolk, VA marshes, Crisfield, MD, and the Little Annemessex River in Maryland. Along the Atlantic Coast they have been reported in Chincoteague, Watt's Bay, Willis Wharf, and Hog Island Bay, VA. No negative impacts have been reported. Complete Record


Veined Rapa Whelks (Rapana venosa)

Veined Rapa Whelks (Rapana venosa) in the Bay is a concern for many, especially clammers.





Veined Rapa Whelks are large snails (~7 inches) native to the Northeast Pacific, from the southern Pacific coast of Russia to the Sea of Japan, Yellow Sea, and East China Sea. These snails have been introduced to several countries including many in Europe and the US. It’s believed that these snails are transported by ships, either in ballast water or hull fouling, but in some areas may have been imported inadvertently with the Pacific Oyster (Crassostrea gigas). Rapa Whelks were first seen in the Chesapeake in 1998, when two specimens were collected in the lower James River near Portsmouth, VA. Since this first discovery, they have become established in lower western Chesapeake Bay from the mouth of the Bay to the mouth of the Rappahannock River and the opposite Eastern Shore but may have moved further up the Bay. More than 1000 individuals have been collected, as well as numerous egg-cases. Because they are very efficient predators, their establishment is expected to have economic impacts on shellfisheries, such commercially important clams (Mercenaria mercenaria). Because of this, there is concern about their potential spread by coastwise ship transport and further range expansion. Complete Record


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