Polycladus gayi is an iconic land planarian found in Chile and locally known as lengua de vaca (cow tongue). Despite being the largest land planarian in Chile and one of the first land planarians to be described, back in 1845, we know almost nothing about its ecology.
However, things are changing! In the past months, two specimens have been found eating in the wild, and, in both cases, the prey was the same species, the giant black snail, Macrocyclis peruvianus, the largest snail in Chile. Both observations occurred in Chilean protected areas, Villarrica National Park and Alerce Costero National Park, and were recorded by nonspecialists visiting the areas. One more important discovery that happened thanks to citizen science!
The land planarian Polycladus gayi attached to snail Macrocyclis peruvianus and feasting on its flesh. Photo by Yerko Lloncón.*
After almost two centuries since P. gayi was discovered, we finally know something about its place in the food chain! And, of course, it also helps us see M. peruvianus from a new perspective since this also seems to be the first record of one of its predators! Even though snails are a common item in the diet of land planarians, not all species feed on them, and we cannot assume that both groups are always directly connected in the food web.
Come see how chubby the planarian got after eating the whole snail!
There is still much more to discover about these two unique Chilean creatures, and the partnership between researchers and the general public is an important way to speed up the process of gathering knowledge about the creatures around us!
Reference:
Boll PK, Lloncón Y, Almendras D (2023) Records of the land planarian Polycladus gayi (Tricladida, Geoplanidae) preying on black snails Macrocyclis peruvianus (Gastropoda, Macrocyclidae). Austral Ecology. https://doi.org/10.1111/aec.13430
A few days ago I saw a photo of some giant African snails and though “that’s an interesting species to feature as a Friday Fellow”, and to my surprise a gastropod was scheduled to be presented today, so voilà, let’s talk about Lissachatina fulica, the Giant African Snail.
As the popular name implies, this land snail is native from Africa, more precisely East Africa, around Kenya and Tanzania, and it is quite large, with adults measuring 20 cm or more in length and about 7 cm in height. The shell is conical and very hard and has a marmorated brown and white color and a sharp border around its opening.
The Giant African Snail is able to feed on a huge variety of plants and can sometimes even consume dead animals, paper and even stones. As a result, it is very adaptable to new areas and has become invasive in many regions of the world, especially tropical areas in Asia, South America and the Pacific.
These snails are hermaphrodites but when mating they can act only as male, only as female or as both and this is usually related to the size of both snails. If they are similar in size, they transfer sperm to each other. If they have different sizes, the smaller snail act as a male and the larger one as a female. A “female-acting” snail can store sperm up to two years to fertilize eggs as they are produced. Thus, a single mated “female” can create an entire population if transported to a new area as it can lay around 200 eggs per clutch and produce about five to six clutches per year.
The Giant African Snail is edible and used as a food source by some African peoples. A similar species, Archachatina marginata, native from Nigeria, is offered to West African deities which in Brazil led to the development of Candomblé. However, as this species is not found in Brazil, it is replaced by Lissachatina fulica, which has been introduced in this country. Recently it has become considerably popular as a pet as well. This species has also been studied for medical use and an antimicrobial compound has been isolated from its mucus.
Especially due to its use as a food source, but also accidentally, the Giant African Snail has ben introduced in many places around the world and has become a threat to tropical ecosystems because of its voracious behavior, where it competes with native snails for food resources. Due to the need to feed on calcium to build their shell, these snails can also end up eating calcium-rich material in buildings and cause severe damage to the structures.
A specimen in Salvador, Brazil. Photo by Clara Matos.**
More than that, the Giant African Snail can harbor a parasitic nematode, Angiostrongylus cantonensis, which causes a very serious meningitis in humans. Most cases of humans being infected by this nematode is the result of eating the snails raw, but there is a small chance of getting infected even by only manipulating the snails.
Due to so many damaging outcomes from the introduction of this species around the planet, it is considered one of the top 100 invasive species of the world. Some attempts to control invasive populations using biological agents have failed miserably and only worsened the whole scenario. Next week I will present one of those failures.
Graeff-Teixeira, C. (2007). Expansion of Achatina fulica in Brazil and potential increased risk for angiostrongyliasis. Transactions of the Royal Society of Tropical Medicine and Hygiene, 101(8), 743-744. https://doi.org/10.1016/j.trstmh.2007.03.012
Thiengo, S. C., Faraco, F. A., Salgado, N. C., Cowie, R. H., & Fernandez, M. A. (2007). Rapid spread of an invasive snail in South America: the giant African snail, Achatina fulica, in Brasil. Biological Invasions, 9(6), 693-702.
Zhong, J., Wang, W., Yang, X., Yan, X., & Liu, R. (2013). A novel cysteine-rich antimicrobial peptide from the mucus of the snail of Achatina fulica. Peptides, 39, 1-5. https://doi.org/10.1016/j.peptides.2012.09.001
The class Gastropoda, which includes snails and slugs, is only beaten by the insects in number of species worldwide, having currently about 80 thousand described species. Among those, about 24 thousand live on land, where they are a very successful group, especially on oceanic islands.
The Hawaiian Islands alone, for example, have more than 750 snail species and there are more than 100 endemic species in the small island of Rapa in the South Pacific. This diversity is much higher than that in any continental place, but the reason for that is not completely understood.
A land snail of the genus Mandarina, endemic to the Ogasawara Islands, Japan. Photo by flickr user kmkmks (Kumiko).*
One of the most likely explanations for this huge diversity on islands is related to the lack of predators. The most common predators of snails include birds, mammals, snakes, beetles, flatworms and other snails. Most of those are not present in small and isolated islands, which allows an increase in land snail populations in such places. Without too much dangers to worry about, the community of land snails n islands can explore a greater range of niches, eventually leading to speciation.
Unfortunately, as always, the lack of danger leads to recklessness. Without predators to worry about, insular land snails tend to lay fewer eggs than their mainland relatives. If there is no danger of having most of your children eaten, why would you have that many? It is better to lay larger eggs, putting more resources on fewer babies, and so assure that they will be strong enough to fight against other snail species. Afterall, the large number of species in such a small place as an island likely leads to an increased amount of competition between species.
But why is this recklessness? Well, because you never known when a predator will arrive. And they already arrived… due to our fault.
The diversity of insular land nails was certainly affected by habitat loss promoted by humans, but also by predators that we carried with us to the islands, whether intentionally or not. These predators include rats, the predatory snail Euglandina rosea and the land flatworm Platydemus manokwari, the latter being most likely the worst of all.
The flatworm Platydemus manokwari in the Ogasawara Islands. Photo by Shinji Sugiura.
This flatworm arrived at the Chichijima Island, part of the Ogasawara Islands in the Pacific Ocean, in the early 1990s and in about two decades it led most land snail species on the island to extinction and many more are about to face the same fate on this island and on others. Not being prepared for predators, these poor snails cannot reproduce fast enough to replace all individuals eaten by the flatworm.
We have to act quickly if we want to save those that are still left.
Chiba, S., & Cowie, R. (2016). Evolution and Extinction of Land Snails on Oceanic Islands. Annual Review of Ecology, Evolution, and Systematics, 47 (1), 123-141 DOI: 10.1146/annurev-ecolsys-112414-054331
Sugiura, S., Okochi, I., & Tamada, H. (2006). High Predation Pressure by an Introduced Flatworm on Land Snails on the Oceanic Ogasawara Islands. Biotropica, 38 (5), 700-703 DOI: 10.1111/j.1744-7429.2006.00196.x
Here is a list of species described from July 11 to July 20. It certainly does not include all described species. Most information comes from the journals Mycokeys, Phytokeys, Zookeys, Phytotaxa, Zootaxa, International Journal of Systematic and Evolutionary Microbiology, and Systematic and Applied Microbiology, as well as journals restricted to certain taxa.
Pseudoechthistatus sinicus (top) and P. pufujiae (bottom) are two of the 40 new species of beetles described in the last 10 days.
Last week I introduced a land planarian that feeds on land snails, Obama ladislavii, or, as I called it, the Ladislau’s flatworm. Therefore, today, I thought it would be great to present a similar situation occurring backwards: a land snail that feeds on land planarians.
So let me introduce this little predator, the land snail Rectartemon depressus. Again, it is not a widely known species and thus it has no common names, but why not call it the ‘orange jaguar snail’? Species of the genus Euglandina, which are also predatory snails, are called ‘wolf snails’ by comparing them to a common predator in North America. As Rectartemon species are common in South America, we could perfectly call them ‘jaguar snails’, right?
Rectartemon depressus about to capture a land planarian Obama marmorata. Photo extracted from Lemos et al., 2012
Found in areas of Atlantic Rainforest in Brazil, the orange jaguar snail has a yellow to orange body and a whitish shell. It is listed a vulnerable species in the Brazilian Red List, but it is not mentioned in the IUCN’s Red List.
Initially known as a predator of other land gastropods, the orange jaguar snail revealed a new item in its diet recently. During attempts to find the food items in the diet of some land planarians from southern Brazil, the orange jaguar snail was offered as a food option, but while the expectations were that the planarian would eat the snail, the opposite happened! After contacting the land planarian, the snail simply grasps it with its radula (the snail’s toothed tongue) and sucks it in very quickly, just as if it were eating a noodle!
The orange jaguar snail eagerly consumes several land planarians, both native and exotic species. It makes it one of the first known predators of land planarians. One of its prey is the Ladislau’s flatworm, so we have a snail that eats a flatworm that eats snails!
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References:
Lemos, V., Canello, R., & Leal-Zanchet, A. 2012. Carnivore mollusks as natural enemies of invasive land flatworms. Annals of Applied Biology, 161 (2), 127-131 DOI: 10.1111/j.1744-7348.2012.00556.x
Santos, S. B., Miyahira, I. C., Mansur, M. C. D. 2013. Freshwater and terrestrial molluscs in Brasil: current status of knowledge and conservation. Tentacle, 21, 40-42.
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