Monday, October 22, 2012

Moon Snails (Phylum Mollusca: Family Naticidae) of Singapore

The naticids are commonly called the moon snails due to the round shell, nocturnal habits and many species are whitish in colour. The body, when fully extended out of the shell, is proportionally much bigger than the shell as the animal inflates itself with sea water. Part of the mantle (a thin, flap-like extension of their body) covers the shell, protecting it from abrasion and preventing other organisms such as algae or barnacles from growing on the shell. Hence, the shell usually appears smooth without encrusting organisms such as algae or barnacles.

Moon Snail's Trail
Moon snails hunt for small clams and snails in the sand to feed on. They are often seen moving just beneath the surface of the sand. As they burrow, they will spread their foot out wide to detect the prey. Upon detecting the prey, they will enclose the prey with the huge foot, and secrete an acidic to soften the shell, after which they will slowly create a hole on the shell with the radula, and feed on the prey in the shell.

sand collar
Moon snails lay their egg capsules in sand collars, which are basically a flattened and hardened ribbon of egg capsules, sand and mucus, spirally coiled up. The size of the sand collar varies, depending on the species. The above sand collar of an unknown moon snail is about 4cm across.

sand collar
This sand collar is much bigger - about 10cm across.

Tiger Moon Snail (Notocochlis tigrina)
Moon snails practice internal fertilisation, and sometimes mating pairs can be seen on our shores.

Here are the moon snails that I have photographed on our shores so far (thanks to Siong Kiat who gave tips on how to identify them!). 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.

Tiger Moon Snail (Notocochlis tigrina)
The Tiger Moon Snail (Notocochlis tigrina), despite the name, has no stripes but dark brown or maroon pots on its shell. The body of the snail is translucent white in colour.

Pear-shaped Moon Snail (Polinices mammilla)
The Pear-shaped Moon Snail (Polinices mammilla) has a pear-shaped shell, which can be all white or with black and/or orange stains.

Pear-shaped Moon Snail (Polinices mammilla)
Here is one with hardly any stains on its white shell.

Pear-shaped Moon Snail (Polinices mammilla)
The body of the snail is a translucent white.

Polinices sp.
The above features an unknown Polinices sp., possibly a Polinices melanostomoides or Polinices melanostomus. It is hard to determine which is it unless the animal is removed, revealing the shell.

Bladder Moon Snail (Glossaulax didyma)
The Bladder Moon Snail (Glossaulax didyma) has a greyish brown shell, and the spire is marked with a dark spiral band.

Bladder Moon Snail (Glossaulax didyma)
The body of the snail is usually light grey in colour.

Nerite-like Moon Snail (Sinum neritoideum)
The Nerite-like Moon Snail (Sinum neritoideum) is unable to keep its entire body in its shell, and hence most of the time it is seen with the mantle and foot full extended. This species also has a much depressed spire, marked with a dark thin spiral line.

Sinum sp.
This is another Sinum sp. which has it shell entirely concealed under its body, appearing much like a slug!

Yolk Moon Snail (Natica vitellus)
The Yolk Moon Snail (Natica vitellus) is also called the Calf Moon Snail, as the species name "vitellus" can mean "egg yolk" or "calf". The shell is usually a light reddish brown.

Yolk Moon Snail (Natica vitellus)
On the underside, the columella usually has an obvious hole.

Yolk Moon Snail (Natica vitellus)
The body is densely marked with fine brown lines, especially the anterior end.

Zoned Moon Snail (Naticarius zonalis)
The Zoned Moon Snail (Naticarius zonalis) has a shell that strongly resembles the previous species, but the anterior end of the body is marked with fine red spots instead, while the foot is marked with white stripes.

Gualtieri's Moon Snail (Notocochlis gualteriana)
The Gualtieri's Moon Snail (Notocochlis gualteriana) is uncommonly seen on our shores. It has a light brown shell, and translucent white body with maroon or dark brown speckles.

Lined Moon Snail (Natica lineata)
The Lined Moon Snail (Natica lineata) has a shell densely marked with brown stripes on a white background. The body is light brown in colour.

Lined Moon Snail (Natica lineata)
It has a white operculum.

  • 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, 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.
  • World Register of Marine Species. 2012.  Retrieved Oct 19, 2012, from

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