Apple snails belong to the phylum Mollusca, class Gastropoda (snails), subclass Prosobranchia, order Caenogastropoda (Mesogastropoda in older literature), superfamily Ampullarioidae, family Ampullariidae (Apple snails). The whole apple snail family (Ampullariidae) is divided in 7 (or 10, depending of the authority followed) genera [click here to see their characteristics] and contains about 120 different species*. However, much work has to be done to identify all species, to rule out the misidentified species and to remove the synonyms. A list with reported geographical locations of several species is available: [Reported geographical locations 160K].
* New insights in the phylogenetic relationships reduce the actual number of species drastically. See the Pomacea page.
For those who want to identify the apple snails derived from the aquarium trade
First of all it’s important to make sure that you are dealing with an apple snail (obvious). If you are not sure about this, you can check it out here.
In general, it’s quite simple: if you bought your animal from a pet shop, you probably have a Pomacea diffusa apple snail or a snail from the Pomacea canaliculata – insularum group. The latter is a group of very similar and closely related species. In most cases, the offered snail is a Pomacea insularum or a Pomacea canaliculata snail, but occasionally Pomacea haustrum and possibly other species from the canaliculata group, like Pomacea maculata might be available as well.
For the snails of the Pomacea canaliculata – insularum group, it’s quite hard to distinguish the species as the external differences are subtle and the variation within species is high. A possible way do distinguish these snails is the colour of the eggs*. one should also keep in mind that hybrids between several closely related species might occur. This cannot be ruled out in invasive species and those available in the aquarium trade.
Pomacea canaliculata (Lamarck, 1819)
Pomacea insularum (D’Orbigny, 1839)
Pomacea lineata (Spix, 1827)
Pomacea doliodes (Reeve, 1856)
Pomacea haustrum (Reeve, 1856)
Pomacea gigas / maculata (Perry, 1810)
grows over 10cm / 4 inch
* This is based on reported egg colours, and it could well be that even the egg colour varies withing one species. Also the food composition, the development stage of the eggs and the humidity of the air can affect the egg colour.
When the snail has a flat shell and has a size over 2.5 cm (1 inch) with or without dark stripes, you are the owner of a Marisa cornuarietis apple snail (Giant ramshorn snail). This snail is not always recognized as an apple snail due to its different appearance.
Less common, but also occasionally available in the aquarium trade (mainly in the US) is Pomacea paludosa (Florida apple snail).
Below is a quick and dirty guide to identify them based on the shape of the shell. Once more: Ignore the colour of your snails when you try to determine the species by comparing them with pictures. Many colour variations (shell and body) exist within a single species (see photograph on the right) and in the ‘Colour genes’ section.
Sometimes other apple snail species pop-up in the trade, mostly imported species. In these cases, it can be quite difficult to identify them. Try to find out from which region they come as this makes identification much easier.
If you need help to identify an apple snail: feel free to contact me and take some pictures of the snail in such way that the following thing are visible: shell opening (aperture), whole shell shape (including the top), the umbilicus (or measure the size), the sutures of the shell and if available the shell door (operculum). Also measure the size of the shell and if available describe if the operculum is horny (flexible) or calcified.
Have a look at the Pomacea flagellata section to see how a useful picture of the shell looks like.
Notes on the family name (Ampullariidae)
There is a lot of confusion in the nomenclatura of apple snails: the family name is often referred to as Ampullariidae, sometimes as Pilidae (invalid).
In 1758 Linnaeus, who regarded the Ampullariidae as terrestrial, referred Pila ampullacea to the genus Helix. His assumption was based on the fact that he never saw a living example, he only got a shell and thought it to be a terrestial snail.
In 1797 Humphrey attempted to erect the generic name Pomus and described 5 species in this genus. But according to Dall (1904) his work was published anonymous, was not for sale, didn’t bear the name of the author or the name of the publisher and is invalid under the rules of nomenclature. This all makes the generic name Pomus invalid.
In 1798 Röding proposed the generic name Pila (with Helix ampullacea as the type species designated by Dall (1904)).
This genus description did fulfil the requirements of the nomenclature rules, although it was later restricted to the Old World Ampullariidae, with the exception of the West African genera Saulea (Gray, 1867) and Afropomus (Pilsbry and Bequaert, 1927).
In 1799 Lamarck used the name Ampullaria for a single species (Helix ampullacea), making it the type species for Ampullaria by monotypy. However, Dall (1904) designated Helix ampullacea as the type species of Pila rendering Ampullaria Lamarck, 1799 a junior objective synonym of Pila Röding, 1798, despite his designation of Nerita urceus Müller, 1774 as the type of Ampullaria.
In March 1810 Perry created the genus Pomacea (type species Pomacea maculata) in which the American species were placed.
In the same year (1810), a few months after Perry’s publication, Montfort introduced the generic name Ampullarius as an unjustified emendation of Ampullaria. The generic name Ampullarius is a junior subjective synonym for Pomacea Perry, 1810 (accepted by the ICZN, OPINION 13). Unfortunately Ampullarius is still incorrectly used in the aquarium trade.
In 1824 Gray introduced the family name Ampullariidae (type genus Ampullaria Lamarck, 1799), including both the Old and New World taxa.
Preston (1915) introduced the family name Pilidae (type genus Pila Röding, 1798) to replace the family name Ampullariidae, acknowledging the generic name Ampullaria Lamarck, 1799 a junior synonym of PilaRöding, 1798.
However to correctly (under the rules of the nomenclatura) replace the family name Ampullariidae with Pilidae a general acceptance is needed (ICZN Code article 40(b)), but as most authors preferred Ampullariidae above Pilidae this requirement hasn’t been fulfilled. The family name Ampullariidae Gray, 1824 should therefore be considered as the valid name and this has been accepted by the International Commission on Zoological Nomenclature OPINION 1913, placing Pilidae Preston, 1915 on the Official Index of Rejected and Invalid Family-Group Names in Zoology.