Can you guess what the similarities are between the objects on the right and the door?
The two white objects are called an operculum and they are common to most gastropods – the marine snails that have a spiral shell. The operculum is attached to the snail’s muscular foot and when the snail withdraws its body into its shell, the operculum comes in last and fits snuggly into the opening of the shell. In doing so its acts just like a door, a physical barrier between the outside and inside of the shell. The pictures above show both sides an operculum, the flat side is attached to the snail, the convex side faces out.
The operculum pictured below is from a snail called a Warrener and it is a common sight on Mornington Peninsula back beaches. It is made of a hard shell-like substance that remains intact after the animal dies. Most other snails that have an operculum which is made of a thin horny material which decays when the animal dies.
The operculum plays two important roles in the survival of the gastropods. It allows the animal to seal its shell when faced with a threat such as a predator and gastropods living in the intertidal zone use it to seal their shell to prevent drying out during periods of low tide as you can see in the picture below.
Watch this amazing clip that shows a snail popping out of its circular operculum (trap door).
If you would like to learn more about the amazing world of marine snails and other fascinating invertebrates that live around the rocky intertidal, and/or join us on an awesome rockpool ramble when restrictions ease please do not hesitate to contact Dolphin Research Institute’s Education Director, Mandy Robertson on firstname.lastname@example.org