A NSW Government website

New Zealand screwshell


The New Zealand screw shell (Maoricolpus roseus) 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.

The New Zealand screw shell 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.


If you think you have seen a New Zealand screw shell in NSW, please take several high resolution photos or collect a sample and freeze in a plastic bag and report your sighting. For identification photos should show:

  1. Shell size - please include something for scale if possible
  2. Key features such as shell colour and markings

Note the location and, if possible, record GPS points.


New Zealand Screw Shell - a long and skinny conical white and brown shell. key features:

  • Up to 91mm in length, commonly 60-70mm
  • Colour fawn to reddish or purplish brown, marbled or streaked in darker brown
  • Smooth spiralled cone (no beads)
  • Conical shell

Know 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.

Native screwshell, Gazameda speciesNative 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

Mud whelkMud 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

Hercules club whelk (Pyrazus ebeninus)Hercules club whelk

Key features:

  • Up to 11cm long
  • Dark brown shell with flaring lip


  • Mudflats and mangrove swamps in esturies