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.

Don't pierce holes with this awl - Subulina octona (Subulinidae)

The next species of snail host extraordinaire first came to my attention as the first intermediate host of the feline trematode Platynosomum fastosum. It is known as the miniature awl snail or by its binomial name Subulina octona.

Subulina octona was originally native to the tropical parts of the Americas and the Caribbean. However, the current distribution is extensive due to introductions into other parts of the world. The snail has been reported in Europe (Denmark, Germany, Czech Republic), Sri Lanka and several island nations of Oceania such as Fiji, Samoa, Vanuatu etc. Whether the introductions were accidental or deliberate is currently unknown.

Subulina octona
By Luis Ruiz Berti, Creative Commons
CC BY-SA via Wikimedia

If you were to come across this terrestrial, air breathing snail you would observe the following. Subulina octona is an elegant, small snail measuring only 1.4 - 1.7 cms. The thin, glossy, pale yellow to brown shell is narrow, tapering and long with 8 - 11 whorls ending in an ovate aperture.

S. octona live in moist ground litter in forests but are also capable of thriving in greenhouses and hothouses. A distinctive feature of the life history that D'avila et al. record in their 2018 article involves "egg-retaining", which refers to a reproductive phenomenon in which a major part of the embryonic development occurs inside the body of the parent snail, and the egg when laid has a well-developed embryo. This strategy along with a long life span, several reproductive events per year and high survival of juveniles all result in S. octona being a successful invader.

This snail has an impressive ability to host parasites whose identities span both helminth phyla. It plays the role of intermediate host to trematodes, nematodes and cestodes including:

(1) Postharmostomum gallinarum, the cecal fluke of chickens, the life cycle of which involves S. octona and was worked out in Hawaii as early as 1940 by Dr. Joseph Alicata.

Subulina octona
By Bruguière, 1789 - Naturalis
Biodiversity Center,
Creative Commons CC0 via wikimedia

(2) Tamerlania bragai, the kidney fluke of domestic pigeons, the life cycle of which involves S. octona andwas worked out in Puerto Rico in 1945 by Dr. Jose Maldonado.

(3) Angiostrongylus cantonensis, the rat lungworm, which typically uses slugs and snails of other genera. A very interesting paper from Brazil by Caldeira et al. records S. octona as a naturally infected intermediate host of the A. cantonensis, harboring on average 20 L2/L3 larvae per snail.

(4) Angiostrongylus vasorum, the french heartworm: A paper published by Bessa et al. shows that S. octona infected with A. vasorum were capable of infecting a dog in an experimental setting, resulting in a patent infection in 49 days.

(5) Davainea proglottina: Cysticeroids of the poultry cestode Davainea were found in S. octona in Cuba. There was also a unique seasonal variation recorded by Perez et al, who observed cysticercoids only in February, May and August.

The wackiest thing about this snail is that there are sources (listed on the first page of a Google search) which sell awl snail adults for 2 Euros each (as of March 28, 2020). Buying and shipping this snail to your location is a terrible idea because it is a highly invasive species and considered an agricultural pest. There is certainly much ink spilled on the terrifying effects of introducing invasive species to novel non-native habitats, and the practice is not commendable.


References:
Title reference: The title of this post is a play on the common name of the snail (Miniature awl snail) and the small pointed tool used for piercing holes called the awl.

Juřičková, L. U. C. I. E. "Subulina octona (Bruguière, 1798)–a new greenhouse species for the Czech Republic (Mollusca: Gastropoda: Subulinidae)." Malacologica Bohemoslovaca 5 (2006): 1-2.

D’ávila, Sthefane, et al. "Life history of Subulina octona (Brugüière)(Gastropoda: Pulmonata: Subulinidae) based on four-year laboratory observations and a comparative histological analysis of egg-retaining and ovoviviparous subulinids." Journal of Natural History 52.23-24 (2018): 1551-1569.

Alicata, Joseph E. "The life cycle of Postharmostomum gallinum, the cecal fluke of poultry." The Journal of Parasitology 26.2 (1940): 135-143.
Maldonado, José F. "The life cycle of Tamerlania bragai, Santos 1934,(Eucotylidae), a kidney fluke of domestic pigeons." The Journal of Parasitology 31.5 (1945): 306-314.

Caldeira, Roberta Lima, et al. "First record of molluscs naturally infected with Angiostrongylus cantonensis (Chen, 1935)(Nematoda: Metastrongylidae) in Brazil." Memórias do Instituto Oswaldo Cruz 102.7 (2007): 887-889.

Bessa, EC de A., et al. "Biological development of Angiostrongylus vasorum (Baillet) Kamensky (Nematoda, Metastrongylidae) in Subulina octona Bruguière (Mollusca, Subulinidae) in laboratory conditions." Revista Brasileira de Zoologia 17.1 (2000): 29-41.

Perez, A., et al. "Seasonal dynamics of the cysticercoids of Davainea proglottina in the intermediate host Subulina octona." Revista Avicultura, Cuba 24.3/4 (1980): 223-225.