Overview
There are ten major groups of molluscs, eight of which are still living; the other two are known only from fossils. These groups make up the 200,000 and more living species of mollusc.
- Caudofoveata (deep-sea worm-like creatures; about 70 species); now generally recognized as a subgroup of Aplacophora.
- Aplacophora (solenogasters: deep-sea wormlike creatures; about 240 species)
- Polyplacophora (chitons: about 600 species, rocky marine shorelines)
- Monoplacophora (deep-sea limpet-like creatures: 29 living species)
- Bivalva (clams, oysters, scallops, mussels: more than 8,000 species)
- Scaphopoda (tusk shells: more than 500 species, all marine)
- Gastropoda (snails and slugs: total estimated at 40,000 - 150,000 species)
- Cephalopoda (squids, octopuses, nautilus, cuttlefish: about 1000 species, all marine)
- Rostroconchia (extinct: probably more than 1,000 species; probable ancestors of bivalves)
- Helcionelloida (extinct: snail-like creatures)
Although diverse morphologically, molluscs exhibit a variety of common characteristics, including a soft body surrounded by some sort of an outer shell secreted by the mantle and a strong muscular foot used for locomotion. The shell may be external or internal or secondarily lost.
All of the eight groups of living Mollusca are represented in New Zealand waters. Approximately 4,700 species of molluscs occur in New Zealand waters, with nearly all represented in Te Papa's collection.