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| shelled snails text index | photo index |
| Phylum Mollusca > Class Gastropoda |
| Nerite
snails Family Neritidae updated Dec 08
Where seen? These snails with thick, rounded shells are common in our mangroves and rocky shores. Some colourful nerites are hard to spot as they blend well with the equally colourful rocks they are found on. They are usually immobile at low tide during the day. At night and on a cool wet day, you might see them creeping about. A recent paper (2008) by Tan and Clements based on surveys of 31 sites over a period of 10 years reveals 19 species with 6 new records for Singapore! Features: 2-4cm. In most nerites commonly seen, the shell is a distinctive semi-spherical, globular shape, somewhat like half a marble. The shell is quite thick and heavy. The streamlined shape probably helps the snail stay on a slippery wave-washed rock. It probably also make it difficult for a crab (or even a human) to grip the shell. A sturdy chalky operculum provides a secure seal to the shell opening. The operculum has an internal peg to lock it firmly. This makes it difficult for a crab to stick a pincer in and dig out the snail. It also protects against water loss during low tide. Nerites usually stay above the high tide line. This is probably to avoid being eaten by fish. They have long thin tentacles and most have handsomely striped bodies. A preliminary identification of the various species of nerites can be made by looking at the teeth-like structures at the shell opening (these do not actually function as teeth to chew food), and the general shape and texture of the shell and operculum. But very similar-looking nerites can only be positively distinguished by looking at internal features of the shell and animal. Here's a comparison of some similar nerite snails and how to roughly tell them apart. What do they eat? Nerites graze the algae that thrive on the rocks, scraping this off with their radula. They also eat lichen growing there. They are often found near their food source; areas where sunlight and water exchange are greatest. Nerite babies: Nerites have separate genders and engage in internal fertilisation. They have a complex reproductive system to achieve this, and to produce nutrition-packed eggs in protective capsules. The white circular egg capsules are sometimes seen in rock pools, under rocks and in moist crevices. Each egg capsule may have more than 30 eggs. These hatch into free-swimming larvae that only later settle down to develop into snails. Human uses: Some species of nerites are eaten raw or toasted. Status and threats: The tiny and beautifully marked Dubious nerite snails (Clithon oulaniensis) and Polished nerite (Nerita polita) are listed as 'Vulnerable' on the Red List of threatened animals of Singapore. Like other creatures of the intertidal zone, the rest of our Nerites are affected by human activities such as reclamation and pollution. Trampling by careless visitors and over-collection can also have an impact on local populations. |
 Nerites mating with their white egg capsules. Chek Jawa, Feb 02  Tough shell with thick operculum. Chek Jawa, Jan 05 
The Polished nerite has an operculumthat is smooth, without 'pimples'. Sentosa, Feb 08  Long tentacles and broad foot. Kusu Island, Dec 04 |
Nerite
snails can be very common on our rocky shores.
 Nerites with their white egg capsules. Lazarus Island, Jun 09 |
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| Family
Neritidae recorded for Singapore from Tan, S.K. & Clements, R. (2008) Taxonomy and distribution of the Neritidae (Mollusca: Gastropoda) on Singapore. Zoological Studies 47(4): 481 – 494. in red are those listed among the threatened animals of Singapore Davison, G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened plants and animals of Singapore.
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Links
References
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The Nature Society (Singapore), Singapore. 343 pp.|
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