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Phylum Mollusca > Class Gastropoda > Family Cassidae
Grey bonnet snail
Phalium glaucum

Family Cassidae
updated Jan 2020

Where seen? This beautiful snail was seen on sandy areas near lush seagrass meadows. Elsewhere, they are considered common on sandy bottoms, especially on exposed sand flats and close to dead coral areas. Intertidal and shallow subtidal zones to a depth of about 10 m.

Features: 8-12cm long, elsewhere about 9cm, up to 14cm. Shell typical helmet shape with a large body whorl and tiny spire, thus resembling a bonnet. The shell is smooth and grey without any markings. It has a notch in its shell so that its siphon can be extended vertically upwards like a snorkel, probably allowing it to breathe while it stays beneath the sand to hunt or eat its prey. It has a white body and large yellowish foot which is edged in brown, the operculum is fan-shaped and bright yellow.

On top of a Cake sand dollar.
Cyrene Reef, Aug 11

Notch in the shell for its siphon.
What does it eat? According to Tan, it feeds on sea urchins but according to Poutiers it feeds on sand dollars. On our shores, they have been seen on top of Cake sand dollars, and when the sand dollar is examined, a hole is seen in the sand dollar skeleton. This suggests the snail bored the hole. For more gruesome feeding details, see Family Cassidae.

Baby bonnets: Egg capsules usually form an irregular mass, the result of several females spawning together.

Thick strong foot.
Cyrene Reef, Aug 11

Buried with only its siphon sticking out.
Changi East, Oct 11

Juvenile with less developed shell.
Cyrene Reef, Aug 11
Photo shared by Loh Kok Sheng on flickr.

Human uses: It is collected for food and for the shell trade.

Status and threats: The Grey bonnet is listed as 'Endangered' in the Red List of threatened animals of Singapore. It is threatened by habitat loss and over-collection. The Book states that it has not been seen since the early 1970s and its status needs investigation to determine if there are any remaining populations.
Grey bonnet snail (Phalium glaucum)

Grey bonnet snails on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores


Chek Jawa, Dec 19
Photo shared by Juria Toramae on facebook.


East Coast (G), May 21
Photo shared by Juria Toramae on facebook.


Eating a sand dollar?
Cyrene Reef, May 11
Photo shared by Marcus Ng on flickr.

Kusu Island, May 14
Photo shared by Marcus Ng on flickr.


Links

References

  • Tan Heok Hui and Tan Siong Kiat. 30 November 2016. Grey bonnet preying on sand dollar at Changi. Singapore Biodiversity Records 2016: 166-167.
  • Tan Siong Kiat. 29 Nov 2013. Grey bonnet shell (Phalium glaucum) at Semakau Landfill. Singapore Biodiversity Records 2013: 79.
  • 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.
  • Davison, G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened plants and animals of Singapore. Nature Society (Singapore). 285 pp.
  • Abbott, R. Tucker, 1991. Seashells of South East Asia. Graham Brash, Singapore. 145 pp.
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