Synonyms for Pomacea (Perry 1810) are Ampullarius (Lamarck 1799) and Conchylium (Cuvier 1816).
The New World genus Pomacea inhabits a large geographical area from the southern of the USA to the La Plata Bassin in Argentina.

Taxonomy
Over 100 species are described in the genus Pomacea since 1758. However, the validity of many species is doubtfull and in reality the number of species is much lower. The problem with the taxonomy in Pomacea is thea most species descriptions are based on only a few shells, without a decent detailed anatomical study to descriminate between species. Also the authors often did not take in account the geographical distribution and possible variability within on a single species. A good example of this is the flagellata complex: over 30 species have been described, while nowadays, they are all considered to be varieties of a single species, eventually with 4 sub-species.
Many authors attempted to reduce the number valid species and tried to reclassify similar species into single species. At present, about 50 nominal species are known, but even this number is likely higher than the actuall number in the field. The inevitable question here is: "How do you define a species?". In the old-style conchology, it was not uncommon to classify every variation as a new species. This completely neglects species variability and genetic relationships.
Current insights in genetics, evolution and species variability require an new approach in which new techniques are used to address the classification of the Pomacea genus. This implies the use of DNA and chromosome studies, comparing internal morphology, interbreeding experiments, immunological test and a more statistical based analysis of available data.
The newest insights reduce the number of actuall species and subdivides the Pomacea genus in several clades. Within these clades, several groups are recognized, consisting of species that are very similar and might eventually turn out to be a single species. Below is an overview of the new classification of the Pomacea genus. Keep in mind that this is a hypothesis and is subject to changes.
One of teh lmost striking changes are the recognition that Pomacea bridgesii actually consist of two different species: Pomacea bridgesii (Reeve, 1856) and diffusa (Blume, 1957). This is based on mitochondrial DNA analysis. The effect of this changes is that the common spike-topped apple snail in the aquarium trade should now be considered to be Pomacea diffusa (Blume, 1957).

For a good review articles about the taxonomy of the Pomacea canaliculata groups, check out these references:

• CAZZANIGA, N. J. 2002. Old species and new concepts in the taxonomy of Pomacea (Gastropoda: Ampullariidae). Biocell, 26(1): 71-81.
  Full article on-line available: [Click here]
• Timothy A Rawlings at al. 2007: The identity, distribution, and impacts of non-native apple snails in the continental United States)

Want to identify an apple snail of the Pomacea genus?
There is no complete identification guide available in the literature.
Keep in mind that many species described, might be different forms of a single species. Many descriptions of species are based solely on only a few, empty shells. Colour, banding and shell surface (rough, smooth etc.) are no good identification points as these might vary a lot within a single species. An example of this variation of shell colour can be seen at the Pomacea canaliculata pictures. The height of the spine/body whorl isn't a reliable determinant (especially when having only a few snails available) either as this can differ as well within one species.
For the snails of the Pomacea canaliculata 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*:

* 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.

Species according the 'old' classification system:
Synonyms are marked light-grey, doubtfull and uncertain species are marked grey.

Pomacea amazonica (Reeve, 1856) synonym for Pomacea haustrum (Reeve, 1856) Pomacea aulanieri (Hupé, 1856) Pomacea auriformis (Reeve, 1856) Pomacea australis = synonym for Pomacea diffusa (bridgesii) Pomacea avellana (Sowerby, 1909) Pomacea baeri (Dautzenberg, 1901) Pomacea bridgesii (Reeve, 1856) Pomacea bulla (Reeve, 1856) Pomacea buxea (Reeve, 1856) Pomacea canaliculata (Lamarck, 1819) Pomacea castelloi (Sowerby, 1894) Pomacea catamacensis (Sowerby, 1874) Pomacea cerasum (Hanley) Pomacea cingulata (Philippi, 1852) Pomacea citreum (Reeve, 1856) Pomacea columellaris (Gould, 1848) Pomacea conoldea (Martens, 1899) Pomacea cornucopia (Reeve, 1856) Pomacea costaricana (Martens, 1899) Pomacea cousini (Jousseaume, 1877) Pomacea crassa (Swainson, 1823) Pomacea crosseana (Hildago, 1871) = synonym for Pomacea maculata (Perry, 1810) Pomacea cumingi (Reeve, 1843) Pomacea cuprina (Reeve, 1856) = synonym for Pomacea gluaca (Linné, 1758) Pomacea cyclostoma (Spix, 1827) Pomacea da costae (Sowerby, 1909) Pomacea decussata (Moricand) Pomacea dolioides (Reeve, 1856) Pomacea d'orbignyana (Philippi, 1852) = synonym for Pomacea canaliculata (Lamarck, 1819) Pomacea electrina (Reeve, 1856) Pomacea erogata (Crosse & Fisher, 1890) = synonym for Pomacea flagellata erogata (Crosse & Fisher, 1890) Pomacea erronea (Nevill, 1877) Pomacea erythrostoma (Reeve, 1856) = synonym for Pomacea urceus guyanensis (Lamarck, 1819) Pomacea eumicra (Crosse & Fisher, 1890)  = synonym for Pomacea flagellata flagellata (Say, 1827) Pomacea exigua (Philippi, 1852) Pomacea eximia (Dunker, 1853) Pomacea expansa (Miller, 1879) Pomacea diffusa (Blume, 1957) Pomacea figula (Spix, 1827) = synonym for Pomacea lineata (Spix, 1827) Pomacea flagellata flagellata (Say, 1827) livescens (Reeve, 1856) erogata (Fisher & Crosse, 1890) dysoni (Hanley, 1854) Pomacea ghiesbreghti (Reeve, 1856)  = synonym for Pomacea flagellata livescens (Reeve, 1856) Pomacea gigas (Spix, 1827) = synonym for Pomacea maculata (Perry, 1810) Pomacea glauca (Linné, 1758) Pomacea gossei (Reeve, 1856) Pomacea granulosa (Sowerby, 1894) Pomacea guyanensis (Lamarck, 1819)  = synonym for Pomacea urceus guyanensis (Lamarck, 1819) Pomacea haustrum (Reeve, 1856) Pomacea hanleyi (Reeve, 1856) Pomacea hepataria (Reeve, 1856) = synonym for Pomacea paludosa (Say, 1829) Pomacea hopetonensis (Lea, 1839) = synonym for Pomacea paludosa (Say, 1829) Pomacea immersa (Reeve, 1856) = synonym for Pomacea haustrum (Reeve, 1856) Pomacea impervia (Philippi, 1852) Pomacea innexa (Crosse & Fisher, 1890)  = synonym for Pomacea flagellata flagellata (Say, 1827) Pomacea insularum (D'Orbigny, 1839) Pomacea interrupta (Sowerby, 1909) Pomacea labiosa (Koch)  = synonym for Pomacea flagellata flagellata (Say, 1827) Pomacea lattrei (Reeve, 1856) Pomacea levior (Sowerby, 1909) = synonym for Pomacea lineata (Spix, 1827) Pomacea lineata (Spix, 1827) Pomacea lymnaeformis (Reeve, 1856) = synonym for Pomacea aulanieri (Hupé, 1856) Pomacea maculata (Perry, 1810) Pomacea martinezi (Hidalgo, 1866) = synonym for Pomacea columellaris (Gould, 1948) Pomacea metcalfei (Reeve, 1856) Pomacea miamensis (Pilsbry, 1899)  = synonym for Pomacea paludosa (Say, 1829) Pomacea modesta (V. d. Busch, 1859) Pomacea monachus (Crosse & Fisher, 1890)  = synonym for Pomacea flagellata flagellata (Say, 1827). Pomacea nais (Pain, 1949) (could be a synonym for Pomacea lineata) Pomacea nigrilabris (Philippi, 1851) synonym for Pomacea sordida (Swainson, 1822) Pomacea nobilis (Reeve, 1856)  = synonym for Pomacea urceus (Müller, 1774) Pomacea notabilis (Reeve, 1856)  = synonym for Pomacea paludosa (Say, 1829) Pomacea novaegranadae (V. d. Busch, 1859) Pomacea oblonga (Swainson, 1820-23) = synonym for Pomacea urceus urceus (Müller, 1774). Pomacea olivacea (Spix, 1827)  = synonym for Pomacea urceus olivacea (Spix, 1827) Pomacea oviformis (Deshayes) Pomacea paludosa (Say, 1829) Pomacea papyracea (Spix, 1827) Pomacea pealeana (Lea, 1838) Pomacea pernabucensis (Reeve, 1856) Pomacea pertusa (Sowerby, 1894) = synonym for Pomacea castelloi (Sowerby, 1894) Pomacea petiti (Crosse, 1890) = synonym for Pomacea Asolene petiti (Crosse, 1891) Pomacea physis (Hupé, 1856) = synonym for Pomacea lineata (Spix, 1827) Pomacea physoides (Reeve, 1856) Pomacea pinei (Dall)  = synonym for Pomacea paludosa (Say, 1829) Pomacea platae (Maton, 1809)  = synonym for Asolene platae (Lamarck) Pomacea producta (Reeve, 1856) Pomacea pulchra (Gray) Pomacea puncticulata (Reeve, 1856) = synonym for Pomacea urceus guyanensis (Lamarck, 1819) Pomacea puntaplaya (Cousin, 1887) Pomacea purpurascens (Guppy, 1864) Pomacea quercina (Spix, 1927) = synonym for Pomacea urceus yatesi (Reeve, 1856) Pomacea quinquidensis (Miller) Pomacea reyeri (Cousin, 1887) Pomacea robusta (Philippi, 1852) = synonym for Pomacea columellaris (Gould, 1948) Pomacea rotundata (Say)  = synonym for Pomacea paludosa (Say, 1829) Pomacea rufilineata (Reeve, 1856) Pomacea scalaris (D'Orbigny, 1835) Pomacea schrammi (Crosse, 1876) Pomacea semitecta (Mousson, 1873) Pomacea simplex (Reeve, 1856) = synonym for Pomacea lineata (Spix, 1827) Pomacea sinamarina (Bruguière) Pomacea sordida (Swainson, 1822) Pomacea storeria (Jay, 1839) Pomacea strebeli (Martens)  = synonym for Pomacea flagellata flagellata (Say, 1827) Pomacea swainsoni (Philippi, 1851) Pomacea tamsiana (Philippi, 1852) Pomacea tenuissima (Jousseaume, 1894) Pomacea testudinea (Reeve, 1856) = synonym for Pomacea lineata (Spix, 1827) Pomacea trochulus (Reeve, 1856) Pomacea urceus urceus (Müller, 1774) guyanensis (Lamarck, 1819). yatesi (Reeve, 1856) olivacea (Spix, 1827) Pomacea violacea (Valenciennes, 1833) = synonym for Pomacea flagellata flagellata (Say, 1827) Pomacea yatesi (Reeve, 1856)  = synonym for Pomacea urceus yatesi (Reeve, 1856) Pomacea zischkai (Blume & Pain, 1952) Pomacea zonata (Spix, 1827)

Pomacea diffusa.       Pomacea canaliculata.       Pomacea flagellata.       Pomacea glauca.

Characteristics of the genus Pomacea:

	Shell:	surface:	smooth to rough (growth lines), sometimes malleation
		shape:	cone-shaped, ovoid to almost discoidal
		direction:	right (dextral)
		whorls:	round
		shell-opening (aperture):	oval
		umbilicus:	narrow to wide
		colour:	yellow, dark brown to almost black, with or without spiral bands
	Operculum:	corneous
	Body:	head (cephalic) tentacles:	long
		labial tentacles:	long
		breathing siphon:	long (2.5 times body length)
		colour:	grey to yellow-grey with or without darker spots
	Eggs:	above the waterline

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