Also known as the razor fish, this animal is now taken for food, so is decreasing in numbers.
Razor clam, Pinna bicolor
This one's been dead for a while
It lives in sand and mudflats, mostly buried, but you can get a nasty slash from the edges if you sink onto one in soft mud.
You won't see those edges, but you will feel them
Looks like the bivalves we called “pens” in Georgia.
Yes – I just looked up my copy of the National Audobon Society’s “Field Guide to Seashore Creatures” (which I bought in Atlanta last year), and yours are Atrina species, apparently a synonym of Pinna – so the same genus.
We have “sea pens” here, but they are class Anthozoa (corals and anemones and sea pens). You can see some (probably non-Australian) pics at http://www.oceanwideimages.com/categories.asp?cID=270
Far different from our ( washington state USA) Razor Clams, Saliqua patula. Very difficult to dig, very good eating.