learn only 3 things about them ...
Don't take them off the rocks! They will wash away with
the tide and may die.
Periwinkles do move! But only at high tide or in cool
area around a periwinkle is often grazed bare of algae.
seen? Periwinkles sprinkle the rocks on many of our shores.
They appear dead but are very much alive. At low tide, they are usually
wedged into crevices and cracks in rocks and even inside the empty
shells of dead oysters and barnacles.
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, trunk and even leaves.
hardiest of these must be the tiny Knobbly
periwinkles (Echinolittorina trochoides).
periwinkle's shell is thin. The operculum is thin, circular and made
of a horn-like material.
Some very similar species are difficult to positively identify without
close examination. On this website, they are grouped by external features
for convenience of display
Surviving the low tide: At low
tide, periwinkles attach the lip of the shell to the surface with
mucus then seal the shell opening tightly with a thin, horny operculum.
Don't pick periwinkles off a rock! Left unattached, they may wash
away when the tide comes in and they will die.
What do they eat? Periwinkles
graze on tiny algae growing as a film over the rocks. Some species
even eat algae growing within the rock, and rasp off some rock as
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 where these drift with the plankton as they
develop. Others lay gelatinous egg masses or retain their eggs until
these hatch. Free-swimming larvae hatch from the eggs, only later
developing into snails.
Human uses: In our region, they
are collected for subsistence food by coastal dwellers and for shellcraft.
Large 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. They were
also used as jewellery.
Status and threats: There are
indications that the temperate Edible periwinkle (Littorina littorea)
is being over-collected in some places.
None of our Periwinkles are listed among the threatened animals of
Singapore. However, like other creatures of the intertidal zone, the
rest of our Top shell snails are affected by human activities such
as reclamation and pollution. Trampling by careless visitors and overcollection
can also have an impact on local populations.
may be found together.
Chek Jawa, Aug 05
Like other snails, they have
a broad foot and tentacles.
Chek Jawa, May 05
A thin operculum.
Labrador, May 05
Laying eggs on leaves?
Labrador, May 05
Littorinidae recorded for Singapore
Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist
of The Molluscs of Singapore.
snails seen awaiting identification
Species are difficult to positively identify without
On this website, they are grouped by external features for convenience
malaccana (Knobbly periwinkle snail)=Nodilittorina
Littoraria melanostoma (Black-mouth
mangrove periwinkle snail)
- Tan Siong
Kiat and Henrietta P. M. Woo, 2010 Preliminary
Checklist of The Molluscs of Singapore (pdf), Raffles
Museum of Biodiversity Research, National University of Singapore.
- Tan, K. S.
& L. M. Chou, 2000. A
Guide to the Common Seashells of Singapore. Singapore
Science Centre. 160 pp.
- Lim, S.,
P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life
and Times of Labrador Beach. Division of Biology, School of
Science, Nanyang Technological University & Department of Zoology,
the National University of Singapore. 160 pp.
- Wee Y.C.
and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
National Council on the Environment. 163pp.
- Ng, P. K.
L. & Y. C. Wee, 1994. The
Singapore Red Data Book: Threatened Plants and Animals of Singapore.
The Nature Society (Singapore), Singapore. 343 pp.
- Abbott, R.
Tucker, 1991. Seashells
of South East Asia.
Graham Brash, Singapore. 145 pp.