I think it is a sea sponge, although I stand to be corrected. Taken whilst walking around Henley Beach, near my house. I was specifically beach-combing that day, after reading Chromasia.
These images look fantastic printed as a large canvas. They look even better printed on fine-art or premium paper and framed. I use FotoMoto as the fulfilment partner, who are known for high quality prints and cards. Sharing a photo and sending eCards are free! Just select a link below:

Awesome landscape!
just love the colors and the distant hint of the bridge…
Just saw it’s a 10mm – what lens is it?
It’s a Sigma 10-20mm. Look around on the net for it – quite a good lens for the cost.