May 10, 2008

Sea urchin eaten by helmet shell?

What killed this sea urchin?
A question I didn't think about until venwu225 left this comment on the wildsingapore flickr photo of this sea urchin test:

"you think this could have been killed by a helmet shell? They use muratic acid to dissolve the test of the urchin and leave these characteristic black makings, seen on the edge of the wound. I only read about this predatory relationship in literature, never had the honor of seeing it in real life. So this is speculative".

Here's a close up of the wound and the black markings on it.This is fascinating indeed! I didn't even notice this detail.

Does anyone have any other information on this?

Other information

from Family Cassidae (helmet shells) on the Sea shells of New South Wales website by Des Beechey, Senior Fellow, Australian Museum

"Most helmet shells live buried in the sand by day, coming out at night to feed on echinoderms, especially sea urchins, which they can locate by smell from at least 30 centimetre away. They immobilise the urchin, crawl onto it with the thick skin of the foot providing protection from the spines, and make a hole in the urchin shell by an acidic secretion and by rasping with the radula, and suck out the soft parts."

from Family Cassidae (helmet shells) on Gladys Archerd Shell Collection website at Washington State University Tri-Cities Natural History Museum

"This snail has a dramatic way of feeding on sea urchins. It 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."

Do we have helmet shells on Singapore shores?

Thanks to comments by Ivan and Mantamola, I've looked up the members of Family Cassidae listed for Singapore from Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore. National Council on the Environment. 163pp.

Cassis glauca
Cymatium traquebaricum
Phalium glaucum


Ivan said...

Wow! That is interesting. So there's another huge predatory snail out there...

Speaking of which, have helmet shells been seen on our shores in recent years?

~mantamola~ said...

I came across a hermmit crab at Changi last November that looks like a Helmet shell. If is true, we should have Helmut shells on our shores!

Ria Tan said...

Thanks Ivan and Mantamola for the questions!

I've just added to the post, the list of Cassidae recorded for Singapore from Prof Wee and Prof Ng's book.

Sorry I overlooked this element!

Ivan said...

Ria, I Googled the three names you provided, and I think there may be an error somewhere: all the three species named are bivalves from the Carditidae!

My own Googling for 'Cassidae Singapore' reveals the following species:

Phalium areola (mantamola: Looks like the one in your photo)
Phalium bisulcatum
Phalium decussatum
Phalium glaucum

(As listed on

Ria Tan said...

Oops, you're right Ivan. I was reading off the Carditidae list instead of Cassidae list. Darn sleep deprivation.

I've amended to the list under Family Cassidae.

The Cassidae list is
Cassis glauca
Cymatium traquebaricum
Phalium glaucum

These must be the old names as the book was written in 1994.