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rocky shore

Periwinkle Family Littorinidae Periwinkles are small but resilient snails. Periwinkles can breathe air so they are among the most common snails seen on the rocks above the high tide line. Large groups of periwinkles often form a horizontal band on the rocks as they move with the tides. Some larger periwinkles are found on mangrove trees, clinging on to roots and even leaves on the tree. Surviving the low tide: At low tide, they attach the lip of the shell to the surface with mucus then seal the shell opening tightly with the operculum. So please don't dislodge them from the rock. A periwinkle has a thin, circular operculum made of a horn-like material. Super Sturdy Snails: Knobbly periwinkles (Nodilittorina spp.) have tiny knobs on their shell. Able to withstand high temperatures, they are even hardier than the other periwinkles. They often found so high up on the rocks that they are only wet for a few hours for the few days of high spring tides every two weeks or so. These tough snails feed only during these high spring tides or perhaps when it rains. Periwinkle Food: Periwinkles graze on algae growing on the rocks. Some species even eat algae growing within the rock, and rasp off some rock as they graze! Periwinkle Babies: In periwinkles, the genders are separate and they practice internal fertilisation. The males have a prong-like male organ. Some females shed their eggs directly into the water to drift with the plankton as they develop. Others lay gelatinous egg masses or retain their eggs until they hatch. Free-swimming larvae hatch from the eggs, only later developing into snails. Human uses: Periwinkles are eaten in temperate countries such as England. In fact, the name 'periwinkle' comes from the Old English for 'penny winkle' as they were then sold for a penny per handful. Status and threats: There are indications that the temperate Edible periwinkle (Littorina littorea) is being over-collected in some places.		Periwinkles Knobbly periwinkles Periwinkle on a leaf Crammed into a crevice

quick facts
1-2 cm, very common on the rocky shore and in the mangroves

Classification:
Class Gastropoda
Phylum Mollusca

See also ...
Molluscs in general
Gastropods in general

Links
Periwinkles on eNature.com of the US National Wildlife Federation: fact sheets on a wide variety of temperate periwinkles including Littorina littorea, which was eaten by people in Europe.
Littorinidae on The Gladys Archerd Shell Collection at Washington State University Tri-Cities Natural History Museum website: brief fact sheet on periwinkles with photos
Periwinkles, Conniwinks and Clusterwinks (Littorinids) on Life on Australian Seashores by Keith Davey on the Marine Education Society of Australia website: Fact sheet on these shells and details on various species found in Australia.
How does a periwinkle survive out of water if it has gills? on the Mad Scientist Network website: a lovely answer that explains how gills and lungs work.

Other references

Woodward, Fred, 1993. Identifying Shells. The Apple Press, London. 80 pp.
Fiene-Severns, Pauline, Mike Severns and Ruth Dyerly, 2000. Periplus Nature Guides: Tropical Seashells. Periplus Editions. 64pp.
Tan, K. S. & L. M. Chou, 2000. A Guide to the Common Seashells of Singapore. Singapore Science Centre. 160 pp.
Ng, Peter K. L. & N. Sivasothi, 1999. A Guide to the Mangroves of Singapore II (Animal Diversity). Singapore Science Centre. 168 pp. online version
Abbott, R. Tucker, 1991. Seashells of South East Asia. Graham Brash, Singapore. 145 pp.
Tan, Leo W. H. & Ng, Peter K. L., 1988. A Guide to Seashore Life. The Singapore Science Centre, Singapore. 160 pp. online version
Morten, Brian & John Morten, 1983. The Sea Shore Ecology of Hong Kong. Hong Kong University Press. 350 pp.

a companion website to the chek jawa guidebook website©ria tan 2003 www.wildsingapore.com

a companion website to the chek jawa guidebook
website©ria tan 2003 www.wildsingapore.com