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Had another look at some of the worm beds near low tide today. Found one worm partially out. Was going to dig it up, but a wave washed in before i was able to. Found no other worms when I tried to dig in another bed of worm holes. There are some larger holes interspersed with all the small ones on the raised beds.

A seagull had pulled this worm from one of the worm beds we get along the beach. I gave it a fright and it dropped it. I had tried digging for the worms, but found nothing except for empty tubes (see 7th photo). I am assuming the worm shown is the worm species creating these worm beds. But it may not be. Any suggestions @readgb? I don't think it looks like a Thoracophelia as you thought they may be?

Revisited /observations/2351193, found it again without difficulty.

Second photo has my little finger as a scale, the finger nail is about 11mm at its widest point, so I estimate this beast is about 0.75mm across when closed up.

In these shots we can see it comes out of a sand/shell? encrusted hole (which it can completely withdraw into), but no sign of a closure to the hole.

It withdraws readily when disturbed, but I'm not sure whether light or water movement is what it detects. It didn't seem to react to the white LED light from the camera going on and off.

To the upper left in the 8th photo is something else with numerous fine arms ... just out of focus.

@readgb I hope you can appreciate the difficulty in getting this one to sit still for long enough to take some photos. Given I don't have a permit to collect here, I couldn't place it in ethanol.
Under low intertidal rock resting on small bits of rock, sand and corallina.

These are the webcasters I believe do the majority of the large mucus webs. The webs are much coarser and expansive. They are filled with these tiny long worm animals.

~1.5cm long, web size ~8cm
Shallow subtidal

Maybe Nicidion, but I'd like to hear what @readgb thinks before committing to a genus-level ID. This genus doesn't seem to have any NZ records.

Body mainly colourless, with white patches. Dorsal surface of first peristomial ring reddish. Anterior chaetigers with thin red band. Antennae yellowish-brown, with red band inferior to tips. Median antenna long, equivalent in length to ~3 chaetigers. Palps short, colourless. Peristomial and dorsal cirri mainly colourless, with red band (as in antennae).

Approx. -1 metre, low tide. Under cobble.