A Snail’s Tale: Assessment of Morphological Differences Between Introduced Freshwater Mystery Snails in North America

The introduction of non-indigenous species has led to a decline in biodiversity within freshwater ecosystems in North America. The species Cipangopaludina japonica and Cipangopaludina chinensis, also known as the Japanese and Chinese mystery snails (JMS and CMS), respectively, are invasive to North America. However, identification of the two species is complicated by their overlapping ranges and morphology, potentially requiring genetic testing. Using a morphology-based method of distinguishing between the two species would make identification more efficient and widely accessible than genetic testing. To assess morphological differences, we used Image J to measure genetically confirmed specimens (25 CMS, 41 JMS) collected from the United States and Canada, measuring a series of ratios between points on the snails’ shells. We found that CMS had a shell length (SL) to shell width (SW) ratio of 1.235 ±0.05, while JMS had a significantly larger SL/SW ratio of 1.358 ±0.07 (p <0.001). The ratio of SL to height from the major whorl downwards (bi) for CMS was 1.318 ±0.03, while JMS was significantly lower (1.357± 0.08) (p =0.003). Finally, the ratio of SL to whorl height (ae) for CMS was 1.948 ±0.06, significantly higher than JMS (1.863 ±0.14) (p = 0.004). A Principal Component Analysis showed that the SL/SW ratio was the most important when distinguishing between the two species. Although ratios differed significantly, overlap indicates that morphological methods of identification are ambiguous within a certain range (1.226 - 1.333 SL/SW, 1.272 - 1.376 SL/bi, 1.817 - 2.071 SL/ae), and genetic testing may still be required.