Auckland Museum's experts get you closer to the natural world in your backyard, beach or bush with our five-part series. Today we look at New Zealand's unique sea shells, with marine curator Tom Trnski.
KEY POINTS:
The islands of New Zealand have extremely rich marine biodiversity. This is because New Zealand has been isolated from other land masses for over 80 million years, and so plants and animals have been evolving independently for a very long time.
The closest relatives of New Zealand's marine species are found in eastern Australia, partly because they are connected by marine currents across the Tasman Sea, along which marine eggs and larvae can travel; and also because the last land masses that New Zealand was near before it broke away from Gondwanaland were Antarctica and Australia.
Shells and their relatives (Phylum Mollusca), such as those on display at the museum, show us some of the great diversity in just one group of marine animals.
The great biologist Charles Darwin, during his exploration, deduced that all the shells share a common ancestor.
Over more than 500 million years this common ancestor diversified into a large range of body shapes that include sea shells, scallops and oysters, squid and octopus, sea slugs and snails. They have also spread to fresh water and the land.
There are over 112,000 species of molluscs now living, but many other species have become extinct over time, as recorded in the tens of thousands of species in the fossil record.
Our search
We're looking for three kinds of shells found on the coast of the North Island. But first note the following:
* Do not collect shells with live animals inside.
* If you do pick up a live shell to draw or photograph, return it to the same place and in the same position.
Ram's horn shell (Spirula spirula) Kotakota Ngu
You can collect this one. It is about 20-25mm long, white and fragile. Common on the west coast, but also found on the east coast. This is the internal shell of a small squid that lives offshore at depths of 200m to 2000m.
The chambers in the shell are the buoyancy device that allows the squid to move to different depths in the water without having to swim.
The squid come to shallower waters at night to feed on small animals (plankton) and return to deep water during the night. They live for only one year and die after breeding.
Their shells resemble those of ammonites, a diverse group of spiral-shelled molluscs that became extinct at the same time as the dinosaurs, about 65 million years ago.
Some ammonite fossils are on display in the Darwin exhibition.
Cat's eye (Turbo smaragdus) Ataata.
Draw or photograph only; if you find just the operculum (the lid that seals the opening), you can collect this.
Usually about 50mm long, dark brown to black, commonly found in mangrove forests, inter-tidal rock pools, rocky reefs and even under coastal pohutukawa trees.
Shells that live above the tide remain in the shade and retain water in their shell.
The thick operculum seals the animal inside the shell to protect it from drying out and predators.
Tuatua (Paphies subtriangulata).
Collect if no animal inside. 50-80mm long, common. They bury themselves under the sand along the shoreline of beaches. Tuatua shells are frequently washed up on sandy east coast beaches of the upper North Island.
These are desirable as food, and were collected by Maori along with pipi and toheroa. The shell is thick and white, sometimes with brown or black stains. The point of the shell is off to one side, whereas in the pipi it is centrally located.
The toheroa has a similar shape, but it is bigger (up to 150mm long) and tends to be on high energy beaches on the west coast. They are threatened by overfishing; if you catch these for food or bait, limit your catch to the limits set by the Ministry of Fisheries.
www.fish.govt.nz/en-nz/Recreational/Fishery+Management+Areas/AucklandKermadec+Islands/Shellfish.htm
* Illustrations from Powell's Native Animals of New Zealand, published by Auckland Museum.
About the author
Like most of the curators at Auckland Museum, Tom Trnski may be out in the field rather than sitting behind a desk.
For Tom, his field is one of the most beautiful in the world - the waters of the Hauraki Gulf and the Poor Knights. Tom recently joined the Museum from the Australian Museum, where he worked in research and collection management.
Explore and win a ticket
This summer Auckland Museum is exploring the natural world and encourages you and the kids to do the same.
Their popular exhibition Darwin takes an inspiring look at the life and theories of one of the world's greatest scientists, and Gondwana is a magical theatre and puppet show that takes audiences back 80 million years, when dinosaurs roamed our world.
The museum's experts want to help you become a natural born explorer by suggesting a number of specimens you might find out about over summer.
Bring a photo, drawing or an example (if it's already dead) of your discovery into the Natural History Information Centre and, if it checks out correctly, you win a free child's ticket to the Darwin exhibition (closing this Sunday).
