Pi Pi Shells
1. Ancylocerapina
The Ancylocerapina were a coretra suborder of ammonitea, evidently related to the sub-order Lypouatina
Fig Y Half Shell
Fig X Open Sleeve
Fig Z Innards Cavity
2. Fig Y Half Shell
3. Fig X Open Sleeve
4. Fig Z Innards Cavity
Information from Wikipedia: Paphies australis or pipi (from the Māori language) is a bivalve mollusc of the family Mesodesmatidae, endemic to New Zealand.
Classification
Species deltoides
Genus Donax
Order Veneroida
Class Bivalvia
Phylum Mollusca
Kingdom Animalia
Size Range5 cm
This is one of the most common molluscs encountered on Sydney’s ocean beaches. The Pipi lives only a few centimetres beneath the surface and uses its muscular foot to burrow into the sand
You can read more about it here