New Zealand screwshell


The New Zealand screw shell has a hard, smooth conical shell up to 9cm in length. It is a native New Zealand species that can survive in a range of different habitats, and has established successful populations in New South Wales, Victoria and Tasmania.

It forms a dense covering on the sea floor with live and dead shells at depths up to 100m, and competes with native shellfish for food.


New Zealand Screw Shell

Key features:
  • Smooth spiralled cone (no beads) up to 9cm long
  • Yellow/red-brown in colour, often marbled or streaked
Known locations:
  • Twofold Bay and continental shelf off Merimbula and Bermagui
  • Vic and Tas
  • Lying on, or partially buried in sand, mud or gravel
  • Intertidal to subtidal
  • From 1-130m depth
  • Densely blankets sea floor with live and dead shells
  • Can affect growth of scallops and displace native shellfish



Similar native species

These native species may be confused with this marine pest.

Mud whelk / Velacumantus australis

Key features:
  • Broader, rough spiralled shell
  • Up to 2-5cm long
  • Dull grey colour
  • Soft sediments in sheltered waters, estuaries, mangroves, tidal flats, seagrasses

Native screw shell / Gazameda gunnii

Key features:
  • Shorter shell, up to 5-6cm long
  • More mottled appearance, lighter colouration - white/light brown
  • Has fine beads forming ridges around the shell
  • Inner continental shelf at depths to 140m

Hercules club whelk / Pyrazus ebeninus

Key features:
  • Up to 11cm long
  • Dark brown shell with flaring lip
  • Mudflats and mangrove swamps in esturies

The native Mud whelk, Velacumantus australis

Native screwshell, Gazameda species

The native Mud whelk, Velacumantus australis

What is NSW DPI doing?

On the 1st July the NSW Government implemented the new Biosecurity Act 2015 (the Act). Under this new legislation the New Zealand Screwshell are declared as a notifiable species in NSW under Part 2, Schedule 1 of the Biosecurity Regulation 2017 (the Regulation). Under Part 2, Division 5, Clause 18 of the Regulation it is illegal to possess, buy, sell or move this pest in NSW. Heavy penalties apply for non-compliance.

People are expected to have a basic level of knowledge about the biosecurity risks they might encounter in their normal work and recreational activities. All community members have a general biosecurity duty to consider how actions, or in some cases lack of action could have a negative impact on another person, business enterprise, animal or the environment. We must then take all reasonable and practical measures to prevent or minimise the potential impact.

How can you help?

Learn to recognise, and be aware of, the New Zealand screwshell so that you can report any suspected new sighting.

If you see this pest in NSW, please report it immediately

  • Note the exact location
  • If possible take a photo and/or collect a sample
  • Freeze sample in a plastic bag
  • Report your sighting