#3827 - Rhopalimorpha lineolaris - Linear Sedge Shield Bug
'Club-shaped with little lines' - the clubs being the antennae, and the lines on the adult.
The restored wetland across the road from the geology museum had a lot of these small Shield Bugs feeding on the seedheads of the grasses, rushes and sedges. Such waterside habitat is favoured by the species, but they're also found in tussock grasslands and human-altered scrubland on both main islands.
The adults look like this -
Photo by Saryu Mae, on iNaturalist.
Duntroon, Aotearoa New Zealand