The upper shell is flat and shaped rather like a toe nail, the lower is more bowl like. It is 1-2 cm long. These animals attach to rocks using a strong ligament (the pedicle) which protrudes through the lower shell. They are often found attached in small groups.

They are found scattered on rocks at low tide.

They are filter feeders. They feed and breathe using an unusual ciliated ribbon called the lophopore.

They are not related to bivalve molluscs and have been around for millions of years (longer than bivalve molluscs).

Gordon D. P. (ed) (2009) NZ Inventory of Biodiversity; Vol 1 Kingdom Animalia. Canterbury University Press.