I Saw Sea Shells On The Sea Shore

The problem is that I can't identify these ones.  Can anyone help me?

This, on the other hand, is a Horse Mussel shell and this was only the second time I had seen one.

This isn't a shell it's a star-shaped jellyfish of some sort but I can't find any reference to blue star-shaped jellyfish

And finally a beautiful large starfish:

All the above were found when Pauline and I were out walking on Ruakaka Beach in Northland.

Jellyfish

I'm not a great fan of jellyfish and I am probably far from alone.  On the Mahanga Beach there were lots of tiny blue jellyfish.  I've not managed so far to identify them.  However the last photo is a singularly unpleasant little creature which packs a considerable punch.  As we had all been walking barefoot on the beach and there were a lot of these there was probably an element of luck involved in our pain-free enjoyment.

Blue Bottle Jellyfish or Portugese Man of War