[215] Lymnaea stagnalis, Pond Snail

[215] Lymnaea stagnalis, Pond Snail

Introduction

Lymnaea stagnalis, the (Great) Pond Snail is a … … … a snail that lives in ponds!

Taxonomy

Kingdom – Animals

Phylum – Molluscs

Class – Gastropods (Slugs and snails)

Subclass – Heterobranchia

Infraclass – Euthyneura

Clade – Panpulmonata

Superorder – Hygrophila (Air breathing freshwater snails)

(Order – Hygrophila)

Superfamily – Lymnaeoidea (Just Lymnaeidae)

Family – Lymnaeidae

Subfamily – Lymnaeinae

Genus – Lymnaea

Scientific Name – Lymnaea stagnalis

Name

Lymnaea is latinized from Greek limnaios meaning from a marsh or pool. Stagnalis is New Latin for stagnant water or ponds.

Description

The taxonomy of molluscs is complicated and fluid. There are nearly a hundred thousand species of slugs and snails in the class of Gastropods and [172] Roman Snail is a fairly distant relative of Lymnaea.  I have called Hygrophila a superorder above but it may be also considered as an unranked clade. It’s at the same level as Stylommatophora, which you will remember we called an Order for the Roman Snail.

Wikipedia insists on Hygrophila being a superorder but doesn’t specify anything corresponding to the level of an order. We can at least say that what distinguishes Hygrophila from Stylommatophora is that the eyes are at the base of the tentacles rather than at the tips. There have been at least four revisions of the taxonomy of pond snails in recent time and more may be coming! By the time we get to Limpets in November it may have changed again but I have already finished that post.

Taxonomy within the family Lymnaeidae is equally fluid but all the levels up to Lymnaeoidea are defined by the type species Lymnaea stagnalis.

I won’t be looking at any other pond snails in this post but there some others found in the UK.

Although Lymnaea stagnalis may be called the Great Pond Snail, it does not look large in comparison to common land snails. Its shell shape is very different – elongated and conical at one end and more rounded at the other. Apart from the shell, it looks like a snail and is grey all over.

Like all snails they are hermaphrodite and can mate as male or female (not both at the same time.) I think the last picture above may be mating snails.

They are mainly herbivorous and eat algae and water plants, but will also eat small invertebrates and sometimes smaller pond snails.

Habitat and use

Lymnaea stagnalis is common throughout the Northern Hemisphere. It lives in freshwater – either slowly moving or standing water.

It is common and widespread over England and less common over the rest of the UK.

It has a relatively simple central nervous system and is widely used in experiments to study learning, memory and neurobiology.

Other Notes

You can, of course, search for pond snails in ponds but there are many places that make life easier for you by providing pond dipping opportunities for educational purposes and for entertainment. As you will know by now, I visit Slimbridge and they have easily accessible man-made ponds there that provide excellent environments for pond snails.

See also

There are only two other gastropods in this blog. We have already met [172] Roman Snail and other terrestrial snails. The other one, the Limpet, comes conveniently filed with a crustacean, [313] the Barnacle.

[172] Helix pomata, Roman Snail

[172] Helix pomatia, Roman Snail

Introduction

Helix pomatia, the Roman Snail is the largest snail found in England. It is an air-breathing land snail introduced by the Romans.

It is also known as a Burgundy Snail, Edible Snail or Escargot when used in cooking.

I will also look at Cornu aspersum, the Garden Snail; Cepaea nemoralis, the Grove Snail and other British Snails.

Taxonomy

Kingdom – Animals

Phylum – Molluscs

Class – Gastropods (Slugs and Snails)

Order – Stylommatophora

Family – Helicidae (Typical Snails)

Genus – Helix

Scientific Name -Helix pomatia

Name

Not surprisingly the Roman Snail derives its name from the fact that it was introduced by the Romans about two thousand years ago as a food. The word ‘snail’ comes from Old English and earlier Germanic and Norse roots.

The Latin word ‘helix’ from Ancient Greek denotes something twisted and is used for anything spiral in shape like the shell of a snail.

I can’t find any explanation for ‘pomatia’ but Google Translate suggests that it may from a place called Lens in France or Belgium, perhaps where the species was first defined by zoologists. Sometimes nobody knows where scientific names come from.

Description

I won’t go into a detailed description of a snail with its familiar shell, eyes on stalks, and single large foot that leaves a trail of slime.  Among snails, the Roman Snail is very obvious in its appearance. Apart from its creamy coloured shell and very light-coloured body it’s the largest snail seen in Britain – with a shell up to five centimetres across.

Habitat and use

The Roman Snail is an endangered species but is still found in many countries across Europe. It survives in Southern England only in undisturbed grassy or bushy wastelands.

They used to be eaten both by the Ancient Greeks and the Romans and are still liked in France but cultivation is very difficult.

Other Snails

Cornu aspersum, the Garden Snail is in the same family and also eaten as ‘Escargots.’  For two hundred years it was known as Helix aspersa, in the same genus as the Roman Snail but has now been moved to a different genus. [If you haven’t studied Latin don’t worry about aspersa becoming aspersum. It’s part of the syntax of gender agreement and masculine, feminine and neuter nouns.]

I won’t go into gastropod anatomy but snails are hermaphrodite – simultaneously male and female. If you imagine both male and female sexual organs where you might expect the right ear to be, you have a first approximation of snail reproduction. The snails in the picture above are mating.

Cepaea nemoralis, The Grove Snail (or Brown-lipped Snail or Lemon Snail) is another species that has been moved out of Helix. It is one of the largest and most common snails of Europe and comes in various markings – reddish, brownish, yellow or white, with or without one or two darker bands.

See also

I wanted to include all the British land snails but any attempt at generic taxonomy gets very complicated. Wikipedia describes them as terrestrial, pulmonate, gastropod molluscs, which is not an easy definition. Some groups have gills to breathe underwater and some have a kind of lung that enables them to breathe air but neither of these two types is monophyletic. (That means that evolution has made the same split more than once.)

Snails have diverged so that some live in the sea, some in fresh water and some on land. Some sea snails have lungs and some land snails have gills!

We tend to think of snails as having a large shell into which they can hide, and slugs having no shell. (See [038] Slugs.) There is little otherwise to distinguish these gastropods.

Anyway, a quick Internet search shows that there are about 100-150 types of land snail that may be found in Britain. I’ve tried to identify some of my old photographs but I’m left with some that I can only call snails.

For pond snails see [215].