I think this may be part of this whanau. About 20mm wide.
Found under a rock in the mid intertidal zone.
Washed up in a storm
White flecks on tunic wall
No white flecks on tunic wall
Looks very similar to a tunicate I saw in Port Aransas, Texas: http://www.inaturalist.org/observations/2927279
Biscuit Stars (Pentagonaster dubeni) among Sea Tulips (Pyura spinifera)
Sea Tulips (Pyura spinifera) get their vivid colours from a symbiotic relationship with a colourful sponge (Halisarca australiensis)
Ascidiacea (commonly known as the ascidians or sea squirts) is a class in the Tunicata subphylum of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" made of the polysaccharide tunicin, as compared to other tunicates which are less rigid.