Do you know your bivalve from a univalve?
There are two main groups of shellfish. Bivalves are shellfish, which have two shells like mussels and cockles and univalves, which have a single shells with the common mud snail and paua being well known examples.
Worldwide, univalves are the most numerous with more than 10,000 species recorded so far.
In New Zealand we have at least 500 species.
Bivalves usually attach themselves to one place and stay there for most of their lives while univalves are free and move about searching for food.
The shellfish in the photograph is a bivalve that is known as a volute.
Some of the volutes have beautifully decorated shells and are prized by those who collect shellfish.
Others, like this one are quite plain and often go un-noticed.
These particular volutes have a common name and are known as southern volutes, as they are found south of Cook Strait.
They live below the low tide mark on sand or mud and are carnivores, feeding on small shells and any dead animal matter they can find.
They have a rasping tongue, called a radula, and with this they can bore through the shells of other shellfish and so reach the flesh inside
The three specimens in the photograph became entangled in a set flounder net where they were caught actively feeding on a dead flounder. They were about 8 cm long and were protected by a very tough shell that was difficult to break, even with a hammer.