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Phylum Mollusca > Class Bivalvia
True oysters
Family Ostreidae
updated May 2020
if you learn only 3 things about them ...
Oysters take a long time to grow to a large size.
Valuable pearls do NOT come from the Family Ostreida. Oysters are often vandalised by thoughtless visitors.
Oysters can cause food poisoning.

Where seen? Among our favourite seafood, oysters are often over-collected on some of our more accessible shores. Sometimes, they are merely vandalised by thoughtless visitors. They are common on the rocks and other hard surfaces of many of our shores.

What are true oysters? True oysters belong to the Family Osteridae.

Features: The two-part shell is thick and chalky. In true oysters, the left valve is glued firmly to a hard surface. What we see is the right valve. A layer of barnacles and algae often eventually develops over the right valve so that the oyster becomes hard to distinguish from the rock. Some oysters have spikes on this valve, probably to deter predators such as drills. Other bivalves usually have a foot, to dig with or move about. Being immobile as adults, oysters have lost their foot.

It is hard to distinguish oyster species by their shell shape alone. Their shells can take different shapes depending on the conditions they live in. They are usually identified by internal features of the shell and animal. On this website, they are grouped by external features for convenience of display.

Sometimes mistaken for limpets or barnacles. Here's more on how to tell apart shelled animals found on the rocks.

Oysters often form a distint band
on hard surfaces near the high water mark.

Chek Jawa, Jan 08

All kinds of different animals
may settle among the oysters.

Chek Jawa, Jan 08

Some oysters have spikes on their shells,
perhaps to deter predators.
Berlayar Creek, Mar 09
What do they eat? Like most other bivalves, oysters are filter feeders. When submerged, an oyster opens its valves slightly and sucks in a current of water. It uses its enlarged gills to sieve food particles out of this current. When the tide goes out, it clamps up the valves tightly to prevent water loss.

Oyster babies: Oysters may produce eggs or larvae. Some species may change gender while others are simlutaneous hermaprodites being predominantly male or female depending on the temperature of their environment and availability of food.

Human uses: Oysters are relished by people everywhere as a delicacy. They are also believed to have aphrodisiac properties in some cultures. Like other filter-feeding clams, however, oysters may be affected by red tide and other harmful algal blooms when they are then harmful to eat.

Oyster farming: Oysters have been farmed for centuries. Basically, young oysters are kept in cages or mesh bags and left in the sea until they were large enough for market. It is believed that farming oysters for their flesh happened together with farming them for their pearls.

Got pearl inside? Valuable pearls are found in only a small group of oysters. While other kinds of oysters (and even snails) may produce pearls, these are often not pretty enough to be of commercial value. So please DO NOT vandalise our oysters in the vain hope of finding a valuable pearl.

Status and threats: None of our oysters are listed among the threatened animals of Singapore. However, like other creatures of the intertidal zone, they are affected by human activities such as reclamation and pollution. Trampling by careless visitors and over-collection can also affect local populations of young clams. Oysters on disturbed shores are often vandalised by thoughtless people.

Some True oysters on Singapore shores

Family Ostreidae recorded for Singapore
from Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist of The Molluscs of Singapore.
^from WORMS

  Oysters awaiting identification
Species are difficult to positively identify without close examination.
On this website, they are grouped by external features for convenience of display.
  Plain oysters
Zig zag oysters

  Family Ostreidae
  Alectryonella plicatula

Crassostrea gigas

Dendostrea folium
Dendostrea sandvichensis

Lopha cristagalli

Planostrea pestigris

Pretostrea rosacea=^Dendostrea rosacea

Saccostrea cuccullata
(Spiked rock oyster)
Saccostrea mordax

Striostrea mytiloides

Links References
  • 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.
  • Katherine Lam and Brian Morton. 31 Aug 2009. Oysters (Bivalvia: Ostreidae and Gryphaeidae) recorded from Malaysia and Singapore. Raffles Bulletin of Zoology 57(2): Pp. 481-494.
  • Tan, K. S. & L. M. Chou, 2000. A Guide to the Common Seashells of Singapore. Singapore Science Centre. 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.
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