Worm, echinoderm, critter thing?

Here's another one that has me stumped from the other day. I found this critter living in the sand in Nelson Bay, NSW, Australia at a depth of 10 metres. The arms were approximately 10cm in length.

It has arms similar to that of a brittlestar however it had the behaviour and hole of a sand worm...

It does really look like brittlestar arms. Numerous species are hole dwellers who keeps their bodies down under for protection while waving the arms around for food.