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 Amber snails. [RN] 
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picture. |
 Amber snails only are a little larger than 1 cm. [RN] |
Of all terrestrial snails its the amber snails (Succineidae) that live nearest to water. That got them the reputation of even being amphibious, which is incorrect: Amber snails only live on plants growing in or near the water, but they do not live in the water.
Amber snails are called that way, because of their shell's amber-like light brown colour. An amber snail's shell, glassy in appearance, seems too small for the snail's body, and truly amber snails are not able to withdraw completely into their shell. The shell aperture's rim is sharp and does not have a lip. Similar to the glass snails (Vitrinidae) there are different grades of shell reduction in the Succineidae family, with half slugs as well as complete slugs.
Like the German malacologist Geyer wrote in 1929, amber snails externally resemble pond snails (Lymnaeidae). As well as among those, among amber snails different species also are hard to tell apart, as the size of individual snails in a given population of a species, may vary considerably, depending on the surrounding environmental conditions.
Like all other terrestrial pulmonates (Stylommatophora), amber snails are hermaphrodites, that reach maturity about at the half maximal shell size. Though sperm cells mature before the egg cells, self-fertilisation may occur to enlarge populations. For recombination of genes, though, sexual reproduction and mutual fertilisation is indispensable. The common genera Succinea and Oxyloma subsequently lay about 150 eggs, off which, after 1 to 2 weeks the young hatch. Amber snails may reach 2 years of age.
Their life near the water for amber snail also bears a grave danger: It makes them a suitable intermediate host for different water-dwelling parasites of the Trematoda group. Those flukes and other worms have a larval stage that lives in the water, the miracidium. The terminal host always is a warm-blooded animal, such as a mammal or a bird. The intermediate larval stages, though, the cercariae, live in a snail that has been infected by the miracidia.
 Amber snail [RN].
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A very special example is the distome (Leucochloridium paradoxum), whose terminal host is a songbird.
 Amber snail with sporocyste tubes of Leucochloridium spec. Picture: Christian Fuchs [1]. |
As a miracidium it infects an amber snail and then changes into a cercaria in the snail's main digestive gland. The cercariae gather in long sporocyste tubes, which extend into the amber snail's tentacles, swelling them up. The snail now is unable to withdraw its tentacles, and besides, its behaviour is manipulated: Against its natural habit, the snail is made to crawl out into the open.
The sporocyste tubes wavering and moving in the blown-up tentacles attract birds to rip the tentacles off the snail. That way, the cercariae finally are able to infect their terminal host.
In the bird's digestive tract the cercariae change into adult distomes, which reproduce sexually. Distomes' eggs are then spread by the bird's faeces. In the water, miracidia hatch and then again can infect another amber snail.