Found very close to my previous posting, but I couldn't find it on a subsequent visit (will have to wait for another good low tide now). I think it was growing out and downwards from the rock, under about 0.5m of water at low tide, surrounded by seaweed and paua. I thought the description was like Diadumene neozelanica but it doesn't seem to have extra large inner tentacles.

There is a distinct collar around the top of the column and there appear to be pores on the surface that might emit stinging threads (didn't prod it to find out).

The stripes have a stripe within a stripe - a light coloured line down the centre, different from the previous observation.

About 15mm high.

The first photo displayed here was taken from underneath and I think it appears to glow because of the sunlight coming through the sides of the column from above.