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In a word, what is the San Antonio Shell Club all about? Shells!
By its strictest definition, Mollusca is a branch, or phylum, of the kingdom Animalia,
and is one of ten phylums classified under the superphylum called Lophotrochozoa (the
“crest-bearing animals”).
Mollusca is derived from the Latin term molluscus, meaning “soft”. This is
logical, since all animals classified in the phylum Mollusca feature soft parts. (Another mollusca, I am told,
is also a soft member of the nut family and is found throughout Europe and parts of Asia.)
So what makes a mollusc a mollusc? All molluscs share the following features:
- Every mollusc has a fleshy mantle, featuring a cavity that is used for both breathing and excretion. This mantle
covers, at the least, the entire upper surface of the animal. Not all molluscs have hard shells, but for those who do, the
calcium carbonate that forms the shell is secreted from the mantle.
- Every mollusc features a nervous system that is structured in a manner unique to molluscs and no other animal.
- Every mollusc features at least two paired nerve cords (three in bivalves).
- Every species of mollusc produces eggs.
- In each mollusc, several organs have multiple functions. For example, a mollusc's heart and kidneys (nephridia), which are
important parts of the circulatory and excretory systems, are also crucial to the animal's reproductive system as well. In
bivalves, the gills act as filter systems, but they also produce a water current in the mantle cavity that acts as a part the
animal's excretory and reproductive systems.
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