Rose Bay Discoveries

This afternoon, we all went to Rose Bay for a look into the rock pools and walk along the sand. Pop and Nana came and spent the afternoon with us also.
Zem with Nana, Are they fish??

We found small fish, mud skippers, crabs, shrimp, a type of cone shell and sea dollars.

We also found some sort of caterpillar or centipede buried in the sand. I've tried to search online to find out what is was but haven't come up with much except for this photo from somewhere in the Bahamas.
Here are some of the pictures we took:
What is it?

Is it a centipede or caterpillar...or niether?

We think this is its' mouth.

Zemi got totally soaked and sandy. Azariah was kept safe and dry first on mum's back and then on dad's shoulders (except for a trip by dad as we were going home).

Zemi looking out to sea and feeling the waves on his feet.

Zemi feeling the water washing in and out.

Some of the scenery at Rose Bay.

PS. Thanks Bon and Lindon for your insight. I do believe that it was a Bristleworm.