Photo of the day (29): Merdigera obscura

Merdigera obscura is a terrestrial snail in the family Enidae living from western Europe to Uzbekistan. It has a great scientific name.

Its generic name Merdigera is derived from a French word “merde”, that means faeces and from a Latin word “gerō”, that means bearer. Its specific name obscura is derived from a French word “obscur” and from a Latin word “obscūrus”, that means obscure and probably originally means “over” + “covered”.

Its shell is really covered with faeces and with mud. It serves as a camouflage.

Merdigera obscuraMerdigera obscuraMerdigera obscuraMerdigera obscura Merdigera obscura Merdigera obscura Merdigera obscuraFew other snails from the same family Enidae actively add a camouflage on its shell. For example Napaeus barquini use live lichens.


Allgaier C. (2007). “Active Camouflage with Lichens in a Terrestrial Snail, Napaeus (N.) barquini Alonso and Ibáñez, 2006 (Gastropoda, Pulmonata, Enidae)“. Zoological Science 24(9): 869-876. doi:10.2108/zsj.24.869.

Horsák M., Juřičková L. & Picka J. 2013: Měkkýši České a Slovenské republiky. Molluscs of the Czech and Slovak Republics. Kabourek, Zlín, 264 pp. (in Czech and English). page 82.

gero. Wiktionary, accessed 16 July 2014.

obscure. Wiktionary, accessed 16 July 2014.

How to remove Chaetogaster limnaei limnaei

Chaetogaster limnaei limnaei is a species of a small freshwater oligochaete that is an episymbiont on freshwater snails. It is considered to be ubiquitous.

I have collected one Lymnaea stagnalis and few Stagnicola sp. species in the outdoor shop of various plants including wetland plants and freshwater plants. I noticed tiny white worms on snails later when I put snails into my aquaria.

These worms are predators of various aquatic animals including medically important trematodes. Trematodes parazitises snails as well as humans. These Chaetogaster worms eat larvae (miracidia and cercariae) of trematodes and they are helping to snails in this way. The more Chaetogaster worms are on the snail, the the more intense trematode infection is.

I do not know how many trematodes were in snails or in the environment, but maybe lot of them.

Chaetogaster limnaei limnaei on Stagnicola sp.

Chaetogaster limnaei limnaei on Stagnicola spFrom time to time, I used to watch them and I was waiting for the time when they would multiply and when they will torture snail to death. It did not happen.

One day (do not know it exactly, probably few months later) I noticed that all worms disappeared. I did not know why they were gone.

Later I found the reason in the 1974 thesis. Chaetogaster limnaei limnaei is highly sensitive to temperatures above 24 °C. Such a temperature reduces or completely eliminates these worms. Therefore, If you transport worms from their natural environment to your tropical aquarium, there is no need to worry. If you have aquaria with aquarium heater, they are bound to be killed by high temperature. Worms are killed in summer heat as well.

All other photos show Chaetogaster limnaei limnaei on the same Lymnaea stagnalis specimen.

There does not seem to be anything strange from the general point of view. Nevertheless, there are still many worms on the snail’s body.

Lymnaea stagnalisChaetogaster limnaei limnei on Lymnaea stagnalisThey are in mantle cavity too.

Chaetogaster limnaei limnei on Lymnaea stagnalisDetail of one Chaetogaster limnaei limnaei on the left tentacle of Lymnaea stagnalis.

Chaetogaster limnaei limneiFew Chaetogaster limnaei limnaei on the left tentacle of Lymnaea stagnalis.

Chaetogaster limnaei limneiOne Chaetogaster limnaei limnaei.

Chaetogaster limnaei limneiReferences

Hopkins S. R., Wyderko J. A., Sheehy R. R., Belden L. K., Wojdak J. M. 2013: “Parasite predators exhibit a rapid numerical response to increased parasite abundance and reduce transmission to hosts“. Ecology and Evolution 2013; 3(13): 4427–4438.

Sankurathri C. S. 1974: “Effects of thermal effluent on the population dynamics of Physa gyrina Say (Mollusca: Gastropoda) and its helminth parasites at Wabamun Lake, Alberta“. Thesis, Department of Zoology, The University of Alberta, Edmonton, Alberta, 132 pp.