INUKSHUK

BILATERAL SYMMETRY: BRACHIOPODS

Looking down at the pebbly sand, you see just the wee top of this lovely fossil brachiopod poking out. Glee, delight and wonder follow as you roll it over in your hands and notice how it differs from clams you may be more familiar with.

Clams or bivalves are molluscs, the second-largest phylum of invertebrates with about 85,000 extant species. While brachiopods share some similarities with their molluscan friends they are in a phylum all their own.

Brachiopods are small marine shellfish that are not so common today but back in the Palaeozoic they were plentiful the world over. The two valves that make up a brachiopods shell are of different sizes and if you look closely you'll see that the hinge runs top and bottom  -- versus left and right like a clam.

Their lineage dates back to the Cambrian with over 12,000 fossil species and 350 living relatives sorted between 6,000 genera. There are two major groups of brachiopods, articulate with toothed hinges and simple open and closing muscles to manipulate their shells and inarticulate brachiopods with untoothed hinges and a more complex set of muscles used to control the brachial supports used to open and close their shells.

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