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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: crested ramshorn

Taxonomy: available through www.itis.gov

Identification: Drepanotrema kermatoides’ shell is extremely flat with multiple whorls making a spiral. The shell has numerous close-set, low spiral ridges (lirae) (Thorp and Covich 2010). 

Size: 4-6 mm (diameter; Rumi et al. 2004)

Native Range: Caribbean region, Central America and South America

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Drepanotrema kermatoides are pulmonate snails, which means that they have lungs rather than gills, and they are hermaphroditic. They become mature at year one for 60-80% of the population (Rumi et al. 2007). Reproduction occurs over most of the year in the snail's native range (Rumi et al. 2004, Rumi et al. 2007).

Most often found in streams and rivers (Rumi et al. 2004), the species shows a high tolerance to environmental stress, including low dissolved oxygen environments (Rumi et al. 2007). Drepanotrema kermatoides are limited by saltwater (Vivar et al. 1996).

Drepanotrema kermatoides have been observed to have an affinity for free-floating macrophytes (Rumi et al. 2007).

Means of Introduction: Unknown, but likely a hitchhiker with aquatic plants (macrophytes).

Status: The current status of the introduced populations are unknown. 

Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

References: (click for full references)

Thorp, J.H., and A.P. Covich. 2010. Ecology and Classification of North American Freshwater Invertebrates (Third Edition). Academic Press, Elsevier Inc, San Diego, CA.

Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rosenberg, Barry Roth, A. Scheltema, F.G.Thompson, M. Vecchione, and J.D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: mollusks. Second Edition. American Fisheries Society Special Publication 26.

Rumi, A., D. Gutiérrez Gregoric, M. Roche, and M. Tassara. 2004. Population structure in Drepanotrema kermatoides and D. cimex (Gastropoda: Planorbidae) in natural conditions. Malacologia 45: 453-458.

Rumi, A., G. Gutiérrez, and M.A. Roche. 2007. Growth rate fitting using the von Bertalanffy model: analysis of natural populations of Drepanotrema spp. snails (Gastropoda: Planorbidae). Revista de Biología Tropical 55(2):559-567.

Vivar, R., H. Larrea, P. Huaman, M. Yong, and G. Perera.1996. Some ecological aspects of the freshwater molluscan fauna of Pantanos de Villa, Lima, Perú. Malacological review 29: 65-68.

Author: Daniel, W.M. and Morningstar, C.R

Peer Review Date: 9/27/2019

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.