Practical information to identify and manage non-native, invasive plants and animals
The Quiet Invasion:A Guide to Invasive Species of the Galveston Bay Area
Marisa cornuarietis
| ITIS TSN: | 73195 |
| Presence: | Species of Concern |
| Habitat: | Aquatic |
| Native Range: | South and Central America |
Human Health
This species poses no known human health impacts.Prohibited Lists
This species and all snail species from the family Ampullariidae (except the spiketop apple snail, P. bridgesii) are legally classified in Texas as exotic, harmful, or potentially harmful. No person may import, possess, sell, or place these species into state waters except as authorized by a rule or permit issued by the TPWD.Introduction Pathways
The giant ramshorn snail was most likely released via the aquarium trade.Geographic Distribution
Established populations of the snail were identified in Florida in 1957 and in central Texas in the 1980s. The giant ramshorn snail occurs in central Texas in Comal, Bexar, and Hays counties. It is not currently found in the Lower Galveston Bay Watershed (Karatayev et al. 2009).Specific Primary Habitats
The giant ramshorn snail prefers still or slowly moving freshwater lakes, ponds, irrigation canals and swamps. It prefers shallow, stable water levels and a large amount of leafy plants. This species can survive, although it does not reproduce, in salinities up to 8.5 ppt. The temperature range for this species is between 8-35°C (Karatayev et al. 2009). This is a warm water species, but can tolerate low winter water temperatures. The giant ramshorn snail can inhabit waters with dissolved oxygen contents as low as 0.5 ppm.Ecological, Economic, or Social Impact
The giant ramshorn snail is an aggressive eater and competes with native snails for food. It also feeds on the eggs and young of other snail species. This snail can decimate vegetative cover. In the San Marcos River, M. cornuarietis feeds on the roots of the federally endangered Texas wild-rice (Zizania texana) (Karatayev et al. 2009).Physical Description
The giant ramshorn snail is 18-22 mm wide and 48-56 mm tall. Its shell is 35-50 mm in diameter or larger. The shell is spherical in shape, consisting of 3-4 whorls. The shell is dark yellow to brick red in color, with 3-6 brownish-black spiral bands (Ghesquiere ; USGS 2008).Reproduction Characteristics
Giant ramshorn snails are hermaphrodites, laying their fertilized disk-shaped eggs on vegetation below the surface in a jelly-like clutch. The eggs are 2-3 mm in size and swell up to 4 mm before hatching. As the snails grow inside the eggs, the eggs become transparent and the snails can be seen moving inside each egg (Ghesquiere).Feeding
The giant ramshorn snail is an omnivore which consumes detritus (decaying organic matter), live vegetation, and the eggs and young of other snails (Karatayev et al. 2009).Control
Early detection is key to preventing the spread and establishment of this species and regional/local monitoring or surveillance is essential. Nonnative snails should not be imported alive or released in local waterways. If found in local waters, note the location and notify the TPWD.Lists
This species belongs to the following lists:
Images
To view a larger version of an image, click on the thumbnail. Giant ramshorn snail (Marisa cornuarietis). Photo courtesy of Amy Benson, USGS NAS Database, http://nas.er.usgs.gov. |
 Giant ramshorn snail (Marisa cornuarietis). Photo courtesy of USGS, USGS NAS Database, http://nas.er.usgs.gov. |
 Giant ramshorn snail eggs in a gelatinous mass, (Marisa cornuarietis), 2 days old. Photo courtesy of www.applesnail.net. |