Snail Clone wars - Lymnaea cubensis and other look-alikes (Lymnaeidae)

Lymnaea cubensis
Antonio Alejandro Vázquez Perera
& Susana Perera Valderrama /
CC BY 3.0 via  Wikimedia Commons

The next snail in this series has many synonyms in literature. It has been called Galba cubensis, Bakerilymnaea cubensis, Fossaria cubensis and Lymnaea cubensis. I am going to refer to it as Lymnaea cubensis because the malacologists who have authored the book "Freshwater Gastropods of North America" call it that.  From the veterinary standpoint, L. cubensis is important as the first intermediate host of Heterobilharzia americana (along with another snail - Pseudosuccinea columella) and Fasciola hepatica.

The native range of L. cubensis is North and South America. In the United States, the snail is currently confined to the south and south east regions (The Carolinas, Georgia, Florida, Louisiana, Alabama, Texas, New Mexico and California). Due to anthropogenic introductions, L. cubensis was recorded in Spain by Schniebs et al. in 2018, which was the first time that it had been found in the wild in Europe.

L. truncatula
Francisco Welter Schultes, modified by Michal 
Maňas. Versión actual modified by Veronidae /
CC BY-SA 2.5 via Wikimedia Commons

L. schirazensis
María Dolores Bargues, Patricio Artigas,
Messaoud Khoubbane,  Rosmary Flores,
Peter Glöer, Raúl Rojas-García,
Keyhan Ashrafi, Gerhard Falkner,
Santiago Mas-Coma /
CC BY 2.5 via Wikimedia Commons

The snails are amphibious and are found in the mud in ditches and ponds. It is quite impossible to distinguish L. cubensis from L. truncatula based on shell morphology alone, and malacology training is required to identify the small differences in male reproductive system morphology between the two species as illustrated by Pointier et al. in their 2009 paper.

Interestingly, L. cubensis is not the only snail with striking morphological similarity to L. truncatula. A cryptic species with near worldwide distribution and very similar morphology called L. schirazensis was described in 2011 by Bargues et al. and is very resistant to Fasciola hepatica (i.e. no cercaria are produced). There are some serious complications that result from the identical morphologies of L. schirazensis and L. truncatula. Bargues et al. posit that misidentification of L. schirazensis as L. truncatula has distorted epidemiological data regarding snail susceptibility status to Fasciola. In the future, molecular data would have to be used to confirm  snail morphological identities in cases of cryptic species and the known occurrence of shape and size variations attributable to geography and lineage. PCR + sequencing of the coxI, ITS or 18S genes may help resolve identification problems, since it is well-known that the classification of the Lymnaeidae is fairly complicated (Link here for an explanation).

The capacity of L. cubensis in the transmission of the following is important:
(i)  Heterobilharzia americana: The role of L. cubensis was worked out in the early 1960s by Dr. Hong-Fong Lee. Furcocercous cercariae were shed 4 weeks after infection. Distribution of the trematode closely follows the distribution of its two first intermediate hosts: L. cubensis and P. columella.

(ii) Fascioloides magna: Vignoles et al. found that L. cubensis could be an experimental intermediate host for Fascioloides magna. The role played by the snail in natural infections is still unknown.

(iii) Fasciola hepatica: L. cubensis along with L. viatrix and L. neotropica have been established as the major vectors in Latin America. And while misidentifications of L. cubensis as L. truncatula may not throw-off the snail susceptibility data as much as L. schirazensis, the situation is still not ideal.

So, if you happen to be see a Lymnaeid snail that looks like L. truncatula, remember that identification to species level is very difficult and that the snail before you might not be the species that you think it is.

References:

Schniebs, Katrin, et al. "The first record of Galba cubensis (L. Pfeiffer, 1839)(Mollusca: Gastropoda: Lymnaeidae) from open fields of Europe." Folia Malacologica 26.1 (2018).

Dillon, Robert T. The freshwater gastropods of North America. Freshwater Gastropods of North America Project, 2019. FWGNA press. 

Lee, Hong-Fang. "Life history of Heterobilharzia americana Price 1929, a schistosome of the raccoon and other mammals in southeastern United States." The Journal of parasitology (1962): 728-739.

Vignoles, Philippe, et al. "Lymnaea cubensis, an experimental intermediate host for Fascioloides magna." Folia parasitologica 61.2 (2014): 185.

Bargues, M. D., et al. "Characterisation of Lymnaea cubensis, L. viatrix and L. neotropica n. sp., the main vectors of Fasciola hepatica in Latin America, by analysis of their ribosomal and mitochondrial DNA." Annals of Tropical Medicine & Parasitology 101.7 (2007): 621-641.