85 — Helmet shell, Semicassis labiata

There are a few species of helmet shells (Cassidae) in New Zealand waters. The two most common are Semicassis pyrum and S. labiata. Semicassis pyrum is found throughout New Zealand down to considerable depths (~500m), While S. labiata is a shallow water species found only in the north.

They are also found in southern Australia and South Africa and it is thought that this wide distribution is due to a relatively long planktonic larval stage. The larvae swim/float around in the sea for ages and this enables them to be spread far and wide. 

Semicasis labiata are thought to feed on echinoderms, particularly heart urchins (Echinocardium spp.). Oddly enough, I've not been able to find any published data confirming this, just anecdotal information, so at the moment it seems to be assumed. 

This one was found  emerging from the sand just after low tide at Pilot Bay, Mt Maunganui. This the 'insperata' form, which is lighter in colour than typical labiata, and has a row of knobs on the body whorl of the shell.

Semicassis labiata, emerging from the
sand at Pilot Bay, Mt. Maunganui, 17/11/16.

Semicassis labiata, Pilot Bay
Mt. Maunganui, 17/11/16.

Semicassis labiata, Pilot Bay
Mt. Maunganui, 17/11/16.