BioInvasions Records (2015) Volume 4, Issue 3: 189–194 doi: http://dx.doi.org/10.3391/bir.2015.4.3.06 © 2015 The Author(s). Journal compilation © 2015 REABIC Open Access 189 Research Article Clarifying the identity of the long-established, globally-invasive Physa acuta Draparnaud, 1805 (Gastropoda: Physidae) in Singapore Ting Hui Ng 1,2 *, Siong Kiat Tan 3 and Darren C.J. Yeo 1,2 1 Department of Biological Sciences, National University of Singapore 14 Science Drive 4, Singapore 117543, Republic of Singapore 2 NUS Environmental Research Institute, National University of Singapore, 5A Engineering Drive 1, #02-01, Singapore 117411, Republic of Singapore 3 Lee Kong Chian Natural History Museum, National University of Singapore, 2 Conservatory Drive, Singapore 117377, Republic of Singapore E-mail: ng.tinghui@u.nus.edu (THN), nhmtsk@nus.edu.sg (SKT), dbsyeod@nus.edu.sg (DCJY) *Corresponding author Received: 24 December 2014 / Accepted: 6 May 2015 / Published online: 2 June 2015 Handling editor: Vadim Panov Abstract The freshwater snail identified as Physastra sumatrana has been recorded in Singapore since the late 1980’s. It is distributed throughout the island and commonly associated with ornamental aquatic plants. Although the species has previously been considered by some to be native to Singapore, its origin is currently categorised as unknown. Morphological comparisons of freshly collected specimens and material in museum collections with type material, together with DNA barcoding, show that both Physastra sumatrana, and a recent gastropod record of Stenophysa spathidophallus, in Singapore are actually the same species—the globally-invasive Physa acuta. An unidentified physid snail was also collected from the Singapore aquarium trade. Key words: Physastra sumatrana, Stenophysa spathidophallus, taxonomy, DNA barcoding, alien species Introduction Changes in freshwater molluscan communities, including the introduction of alien species, have followed habitat modification (e.g., dam construction [Köhler et al. 2012]). In Singapore, urban habitats such as reservoirs and canals, which were mostly created or modified from existing rivers and streams within the past half a century, are the main habitats for freshwater molluscs (Clements et al. 2006; Tan et al. 2012). The pre-modified natural inland waters of Singapore were likely too acidic to sustain a high diversity of freshwater molluscs (Johnson 1967), and many species found in Singapore today have been introduced or are considered cryptogenic (i.e., of unknown origin) (Tan et al. 2012). One species that was previously considered to be native (Clements et al. 2006), but whose origin is currently categorised as unknown (Tan et al. 2012), is Physastra sumatrana (Martens, 1897) of the family Planorbidae. It was first described from Indonesia, and is commonly found throughout Singapore among ornamental aquatic plants. In neighbouring Malaysia, the species was first recorded in the 1970’s, and was suspected to have been introduced via the aquarium trade (Sullivan et al. 1977). A species that closely resembles Physastra sumatrana, Stenophysa spathidophallus Taylor, 2003 (Physidae), was described from Singapore, and first collected in 1985 (Taylor 2003). Stenophysa spathidophallus had not been collected in Singapore again since the original record, but was recently ‘rediscovered’ in a public park in Singapore (Ng and Tan 2013). In this article, we clarify that the species thus far known as Physastra sumatrana in Singapore, and the recent report of Stenophysa spathidophallus, are in fact specimens of the globally-invasive Physa acuta Draparnaud, 1805.