EPOW - Ecology Picture of the Week

Miniature Mollusk

New Zealand Mudsnail (Potamopyrgus cf. antipodarum), Family Hydrobiidae
Coromandel Forest Park, North Island, New Zealand

Explanation:  Tinier than the fingernail on my pinky finger is this denizen of cool flowing streams and brackish waters of North Island, New Zealand.  This is the New Zealand mudsnail, a member of mollusk family Hydrobiidae.

New Zealand mudsnails can be quite variable in appearance, shell size, shape, and even ornamentation.  Some can be smooth and some can be spiny.  
  

Smooth form showing some speckled coloration.  

These are quite tiny mollusks, ranging only up to 12 mm (0.5 inches) in length, with most quite smaller.

They are native to New Zealand but have been introduced to North America as an invasive species, although their ecological impact is largely unknown.  They are also naturalized in Australia and Europe.
   

Shell colors and patterns can vary substantially among individuals.
Studies indicate that offspring can differ substantially from their parents, as well.

Spined form of the New Zealand mudsnail.
Related species (Potamopyrgus pupoides and P. estuarinus) never have spines.

This is the cool, clear stream in which I discovered them
clinging to the underside of rocks, in the Coromandel Forest Park
of North Island, New Zealand.
  

We enjoyed a fine summer day sharing the aquatic habitat with our shelled friends!

Acknowledgments:
    My thanks to Michelle Greenwood, Freshwater Ecologist with the National Institute of Water and Atmospheric Research in Christchurch, New Zealand, for identification, and to Steven Pawson for hosting me on the field outing to this lovely spot.