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Anentome helena (Philippi, 1847)

Diagnostic features

The shell is conical with a distinct anterior notch and posterior indentation in the aperture. The sculpture consists of strong widely spaced regular axial ribs  Colour dark brown and yellowish bands. Animal with narrow tentacles with eyes situated on the outside of the base of each tentacle. Possesses a retractile proboscis and a long anterior siphon. Operculum with terminal nucleus.

Classification

Anentome helena (Philippi, 1847)

Common name: Assassin Snail

Class Gastropoda

Subclass Caenogastropoda

Clade Neogastropoda

Superfamily Buccinoidea

Family Nassariidae

Genus Anentome Cossmann, 1901 (Type species Canidia fusca H. Adams 1862; synonym of genusCanidia H. Adams, 1862, preoccupied)

Original name: Melania helena Meder in Philippi, 1847. Philippi, R. A. 1847. Abbildungen und Beschreibungen neuer oder wenig gekannter Conchylien. Cassel. (Th. Fischer), 1-231.

Type locality: Java.

State of taxonomy

This species has been recently transferred from the Buccinidae to the Nassariidae (Galindo et al. 2016).

Biology and ecology

Found in the lower reaches of freshwater areas of rivers on sand and mud. Predator and scavenger, feeding on worms, gastropods and carrion. Animal with separate sexes. The female lays several clear egg capsules which are roughly square in shape. Each egg capsule contains a single egg. The egg capsules are generally laid on solid surfaces and commonly at the base of plants.

Distribution

Native to Southeast Asia, but introduced into aquariums into many parts of the world.

Notes

This is the only known freshwater nassariid. It could become a pest by preying on native molluscs if introduced into natural environments in Australia. There are no native carnivorous freshwater gastropods present in Australia, and such an introduction would therefore be of major concern.

The name Clea is sometimes used for this genus, but is now regarded as a separate genus.

An unrelated species that superficially resembles Anentome is Melanopsis praemorsa (Linnaeus, 1758) from Europe. It is a member of the Melanopsidae and is included in the Cerithioidea along with the Thiaridae. It is, however, somewhat similar to Anentome in outline, sometimes has axial ribs and has an anterior canal in the aperture. This species has been intercepted by Australian Biosecurity.

Further reading

Beesley, P. L., Ross, G. J. B. & Wells, A., Eds. (1998). Mollusca: The Southern Synthesis. Parts A & B. Melbourne, CSIRO Publishing.

Brandt, R. A. M. (1974). The non-marine aquatic Mollusca of Thailand. Archiv Für Molluskenkunde 105: 1-423.

Galindo, L. A, Puillandre, N., Utge, Lozouet, J. P. & Bouchet, P. (2016). The phylogeny and systematics of the Nassariidae revisited (Gastropoda, Buccinoidea). Molecular Phylogenetics and Evolution 99: 337-353.

Mienis, K. H. (2011). Will the uncontrolled sale of the snail-eating gastropod Anentome helena in aquarium shops in Israel result in another disaster for Israel's native freshwater mollusc fauna? Ellipsaria 13: 10-13.

Monks, N. (2009). Assassin Snails and Sulawesi Elephant Snails: Keeping Clea and Tylomelania in the aquarium Conscientious Aquarist Magazine 6: 4.

Newel, M. S. & Bourne, G. B. (2013). The assassin snail, Clea (Anentome) helena (Gastropoda: Buccinidae), as a model for developmental and environmental physiology. Integrative and Comparative Developmental Biology 2013 Annual Meeting, Oxford University Press.

Ng, T.H., Tan, S.K., Wong, W.H., Meier, R., Chan, S-Y., Tan, H.H. and Yeo, D.C.J. 2016. Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLOS One. DOI:10.1371/journal.pone.0161130.

Strong, E. E., Gargominy, O., Ponder, W. F. & Bouchet, P. (2008). Global diversity of gastropods (Gastropoda: Mollusca) in freshwater. Hydrobiologia 595: 149-166.