06 May 2009

Wildfacts updates: Rare snails!

We had no idea just how special these snails were when we saw them during last week's low tide trips.Kok Sheng found a living one of these rather strange looking conch snail (see his blog for more). Just a little earlier, I had seen an empty shell.

Little did we know at that time, that it is listed as Critically Endangered! According to the Red Data Book, it was found near our coral reefs and was present in small numbers until the 1960s. "It was rarely seen since then" and possibly "now wiped out". How AMAZING then, that we saw it!

We knew it's a conch (Family Strombidae) because it had the typical knife-like operculum at the end of its muscular foot. After going through my reference books, I figured that this snail is probably Strombus aratrum or the Dark Diana conch.

There's a long explanation of its common name. According to Abbott, this is a subspecies of S. aurisdianae. 'Auris' means 'ear' and indeed, the beautiful underside of S. aurisdianae may be what the ear of the goddess Diana looks like. The common name of S. aurisdianae is the Diana conch or Diana Ear conch. S. aratrum is more elongate and has a brown-stained shell opening. Thus its common name is Dark Diana conch!

Kok Sheng also found this strange conch snail.
It is obviously also a strombid (Family Strombidae), but I failed to discover what this might be.

During the same trip, I also saw this odd moon snail for the first time. It was really flat compared to the more commonly seen moon snails.
This is probably the Egg-white moon snail (Neverita albumen) because of the deep U-shaped depression on the white underside.

Another special snail that Alicia found on Pulau Hantu some weeks ago was this living Clear sundial snail (Architectonica perspectiva).
It took me a while to find out more about this snail and upload a factsheet about it. Sorry. This snail is listed as 'Endangered' in the Red List of threatened animals of Singapore. The original shores where they were found have been lost to reclamation. So it's very special to see it!

The shell coils form a disc shape with a flat base. This shape allows the snail to burrow through sand to find its prey. Snails of the Family Architectonicidae feed on sea anemones, corals and zoanthids. The mouth region is lined with a tough cuticle to protect against the stings of their prey. Kind of a glove for the tongue. Cool!

More photos and videos of the Clear sundial snail
But Kok Sheng's most fantastic find was this Grey bonnet snail (Phalium glaucum).
The shell is helmet-shaped with a large body whorl, large shell opening 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. When I first saw the siphon sticking straight up from the shell, I thought the snail was creeping past a tubeworm tube!

And what does this amazing snail eat? Snails of the Family Cassidae feed almost exclusively on echinoderms: sea urchins or sea stars, mainly at night and often while both predator and prey are buried in the sand. Snails with heavy helmet-shaped shells eat sea urchins. The smaller Phalium feed on sand dollars.

The Gladys Archerd Shell Collection describes their feeding technique dramatically: To feed on sea urchins, the helmet snail creeps up slowly, raises its heavy shell quite high, then abruptly drops the shell in such a way that the urchin is completely engulfed. Since urchin spines contain a poison, the helmet snail releases a paralytic enzyme from its salivary gland, then it secretes sulfuric acid sufficiently strong to dissolve the sea urchin shell in about 10 minutes before consuming its meal. Wow!

In another description by Poutiers, the snail first squirts neurotoxic saliva over its prey to paralyse the spines. The snail is initially protected from these spines by the thick skin of the foot. Then, the snail pushes its snout through the unprotected anus, or through a hole rasped by radula in the test of the victim which may also be crushed under the weight of the snail.
Indeed, when I first posted a photo of this sea urchin test (skeleton) on my flickr, venwu225 commented that the hole might have been created by the acid produced by a Helmet snail. So we really shouldn't have been that surprised to find this beautiful helmet snail during the recent explosion of sea urchin populations on the shores.

Sadly, the Grey bonnet is listed as 'Endangered' in the Red List of threatened animals of Singapore, due to habitat loss and over-collection. The Red Data 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". Wow! Have we found a population? This certainly is most exciting.

It motivates us to keep exploring and to look more closely for the more hidden treasures on our shores!

Though I'm barely recovered, I'm already looking forward to another thrilling but exhausting series of back-to-back predawn trips starting this weekend until Thursday.

More links
References
  • Gastropods by J.M. Poutiers on the FAO website (PDF file).
  • The Gladys Archerd Shell Collection at Washington State University Tri-Cities Natural History Museum website: brief fact sheet with photos.
  • Tan, K. S. & L. M. Chou, 2000. A Guide to the Common Seashells of Singapore. Singapore Science Centre. 160 pp.
  • Abbott, R. Tucker, 1991. Seashells of South East Asia. Graham Brash, Singapore. 145 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.
  • Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore. National Council on the Environment. 163pp.

2 comments:

  1. Wow! These are extremely exciting finds. Just goes to show that there's so much more to discover about our snails.

    I'm sure the malacologists (snail experts) will have a field day if they ever visit Singapore.

    ReplyDelete
  2. Yes, indeed it's most exciting! Unfortunately, it took a while for me to figure out the snails. Resulting in further excitement after the fact.

    We miss you and hope you can join us soon on our explorations!

    ReplyDelete

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