258 species of molluscs are recorded in the mangrove and intertidal areas of Pulau Semakau, through surveys by Project Semakau and reported in Nature in Singapore of the Raffles Museum of Biodiversity Research.
This includes snails, slugs, clams! Not to mention octopus and 'sotong'.
In Science-speak, these included: one polyplacophora species, 97 bivalvia species (30 families), 155 gastropoda (48 families), and five cephalopoda (five families).
A cuttlebone and an empty Nautilus pompilius shell also offer intriguing possibilities.
There's also a great GIS map of Pulau Semakau in the article.
Download and read the article from Nature in Singapore: Tan, S. K. & R. K. H. Yeo, 2010. The intertidal molluscs of Pulau Semakau: preliminary results of “Project Semakau”. Nature in Singapore, 3: 287–296. [PDF, 200 KB]
Although there are no photos in the Nature in Singapore article, you can have a look at some photos on the Project Semakau site.
More about Pulau Semakau and about Singapore's molluscs on wildsingapore.