ARTICLE 131    2015

FROM OYSTER-EATING SHELLFISH TO

PEOPLE EATING COCKLES 

by Jenny Edwards

 

During the last school holidays scores of children and adults gathered at Narooma to get a closer look at some of the animals that live under and beside the wharf.  One of the more unusual finds brought ashore for people to get a closer look was a Giant Hairy Triton or Whelk (Cymatium parthenopea).  It is not clear why it’s called a “giant” -  it only grows to a maximum length of 15cm.  Oyster farmers, especially those in southeast Queensland and along the north coast of NSW, are very familiar with this mollusc because of its appetite for their product. 

 

Despite being regarded as a pest by the oyster farmers, the shellfish has some fascinating features.  When the animal is alive its shell is covered with an outer layer, the periostracum, made of conchiolin.  For the organic chemists among you, this is a quinone-tanned, horny mixture of proteins and complex sugars.  Instead of being a smooth layer the periostracum is raised into many “hairs” or bristles providing the triton with the perfect camouflage when it shelters in rocky crevices among similar coloured seaweeds. 

 

The animal itself is quite spectacular, having a cream-coloured body with numerous brown spots.  

 

The triton is sometimes called the Hairy Oyster Drill or Borer but these names are not really accurate.  It does not bore into the shell of its prey, instead it somehow paralyses the oyster causing the shells to gape and allowing it to be easily eaten. 

 

Like its near relative, Spenglers Triton, which is often seen on cunjevoi, the Hairy Triton has very distinctive egg masses that, when they are washed ashore, often puzzle beach-combers.  They look a little like half a tennis ball but the outside is papery and inside are many small, semi-transparent capsules containing the eggs.    

 

The eggs of the Giant Hairy Triton hatch into swimming larvae which remain in the plankton for over three months, sometimes much longer. It’s probably for this reason that this species is found world-wide.  

 

Cockles

Young Giant Hairy Triton on show at Narooma wharf

 

Photo - Rob Richardson