Tuesday, October 23, 2012

Periwinkles (Phylum Mollusca: Family Littorinidae) of Singapore

The periwinkles are a diverse group of snails commonly found on the upper shores, either on rocks, trees or seaweed. They generally have a smooth columella (the inner side of the aperture or doorway) and thin operculum. The shape of the shell is somewhat pear-shaped, and most species have a tall spire with several whorls. They are usually inactive, being exposed to more heat on the upper shore, and hence they are very heat tolerant. The species on high rocky shores feed on algae but usually only during the high spring tide. The ones on the trees usually feed on the film of algae growing on the leaves and bark. They are able to breathe air with their simple lungs, modified from the mantle cavity. Some species can be confused with the planaxids, but their shells are thinner.

Here are the periwinkles that I have seen so far (thanks to Siong Kiat who gave tips on how to identify them!). The periwinkles are among my most under-photographed groups of snails, and most of the photos below of specimens in the museum. Hence, there is certainly a lot of room for improvement. You may want to take a look at my diagram on the parts of a snail's shell if you are not familiar with the names of the parts, so as to better understand the terms used below.

Echinolittorina malaccana
This periwinkle, Echinolittorina malaccana, has spiral rows of small nodules around the whorls. It is usually found on rocks, growing to about 1cm long.

Littoraria vespacea
This periwinkle, Littoraria vespacea, usually has a brown stain on its columella. The outer lip is slightly translucent, showing some of the patterns on the outer side of the shell.

Littoraria vespacea
There are black bands radiating down from the apex to the base over a cream-coloured background. It is usually found on mangrove trees, growing to about 1cm long.

Littoraria intermedia
The very similar-looking Littoraria intermedia has a columella with a brown outer margin. The brown bands radiating down from the apex over the shell are less defined, and the background colour is whitish and yellowish. The outer lip has distinct brown and white stripes. It is about 1cm long.

Littoraria pallescens
This periwinkle, Littoraria pallescens, has an obvious thicker spiral cord, sometimes of a different colour tone, running over its body whorl. It is commonly found on mangrove trees, growing to about 1.5cm long.

Littoraria pallescens
The colour is very variable though.

Conical Periwinkle (Littoraria conica)
The Conical Periwinkle (Littoraria conica) appears more conical with a distinct, angular bulge on the body whorl. A band of brownish stain can be seen on the columella.

Conical Periwinkle (Littoraria conica)
It is usually found in the mangrove, growing to about 2cm long.

Carinate Periwinkle (Littoraria carinifera)
The Carinate Periwinkle (Littoraria carinifera) has brown dotted lines on the shell over a bluish/greyish background. The aperture is black with a few whitish stripes.

Carinate Periwinkle (Littoraria carinifera)

It grows to about 1.5cm long, and is usually found on mangrove trees.

Black-mouthed Periwinkle (Littoraria melanostoma)
The Black-mouthed Periwinkle (Littoraria melanostoma) has a distinctive black inner lip. The shell is cream-coloured with numerous brown markings.

Black-mouthed Periwinkle (Littoraria melanostoma)
It is often found on mangrove trees, growing to about 2cm long.

Snails from other families that resemble periwinkles:

Snails from the family Planaxidae, such as the Furrowed Clusterwink (Planaxis sulcatus) above is about the same size and shape as many periwinkles. They can be differentiated by the much thicker and more solid shells.

  • Abbott, R. T., 1991. Seashells of Southeast Asia. Graham Brash, Singapore. 145 pp.
  • Oliver, A. P. H., 2012. Philip's guide to seashells of the world. Philip's, London. 320 pp.
  • Tan, K. S. & L. M. Chou, 2000. A guide to common seashells of Singapore. Singapore Science Centre, Singapore. 168 pp.
  • Tan, S. K. & H. P. M. Woo, 2010. A preliminary checklist of the molluscs of Singapore. Raffles Museum of Biodiversity Research, National University of Singapore, Singapore. 78 pp. Uploaded 02 June 2010.
  • 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.
  • World Register of Marine Species. 2012.  Retrieved Oct 3, 2012, from http://www.marinespecies.org.

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