Animal Phyla/Mollusca
- Mollusca
- Name Meaning: Thin shell
- English Common Name: Mollusks or molluscs
- Major distinguishing characteristics: Muscular foot and Mantle, round shell
- Approximate number of species described: 85,000
Natural History
[edit | edit source]Mollluscs are so diverse that it is difficult to set out a single natural history for them. They live in marine, freshwater, and terrestrial environments. There are herbivores, carnivores, and omnivores. There are active predators and filter feeders.
As adults some are highly mobile, and some are sessile and never move once they set down.
Taxonomy
[edit | edit source]There are 8 living classes of Mollusc.
- Gastropoda (snails)
- Bivalvia (clams, etc.)
- Polyplacophora (chitons)
- Cephalopoda (octopuses and squid)
- Scaphopoda (tusk shells)
- Solenogastres
- Caudofoveata
- Monoplacophora
Anatomy
[edit | edit source]Molluscs are highly diverse, but all have a mantle that has a cavity used for breathing and excretion (and secretes the shell in species with shells).
Non-bivalves have a radula, which is a hard structure that rasps food into the mouth.
The Fossil Record
[edit | edit source]There are between 60,000 and 100,000 additional species. Good evidence exists that the gastropods, bivalves, and cephalopods were around by the Cambrian (541 to 485.4 million years ago).