Normally the zone between the black streaks on the dorsum is red (see http://www.seaslugforum.net/find/runnkati), so it has a fanciful resemblance in terms of colouration to a tiny katipo spider.
Pale Triphorids (Bouchetriphora pallida). They eat sponges, but I have no idea why they should be clustering like this. The special thing about triphorids (family Triphoridae) is that their shells coil in a left-handed spiral and you can see this clearly on the one with its animal extended showing its eye. Its shell opens to the left of the centreline, whereas all other gastropods coil in a right-handed spiral.
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