74 — Butterfly chiton, Cryptoconchus porosus

Cryptoconchus porosus, under a bridge
along Auckland's Tamaki Drive, 19/10/16.

The butterfly chiton, Cryptoconchus porosus (Burrow, 1815) is named after its internal shell plates, which when separated from the animal look a bit butterfly-shaped. It is a medium–large chiton (to ~75 mm), and is found throughout New Zealand, at and around the low tide mark. Apparently, there's also a record from Madagascar, but this seems unlikely. They can be variously coloured, from dark greeny-purple to bright orange.

One of the internal valves of a butterfly chiton.
Piha, 2017. This valve is a bit worn and
would sit the other way around when
inside the chiton.

Chitons are molluscs (Class: Polyplacophora) and posses a slug-like body, within which are eight shelly plates. These plates give the chiton great flexibility and enable them to cling on to rocks in places of great wave exposure. In most species of chiton these plates are exposed and easy to see. But in C. porosus they are almost completely enveloped by a fleshy girdle and only visible as a centre line down the back of the animal.

Cryptoconchus porosus, under a bridge
along Auckland's Tamaki Drive,
with compound ascidians, 10/08/15.

Cryptoconchus porosus tends to favour areas with clean moving water, so they are common on wharf piles and under bridges. It is thought that they may graze on sponges, but this has not been confirmed. Spawning occurs during the winter months and is lunar synchronous.

Cryptoconchus porosus, under a bridge
along Auckland's Tamaki Drive,
with athecate hydroids, 2015.