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Go to the key ---INDEX---
Major Phyla
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General fossil discussion
Geologic time
Phylum BRACHIOPODA (Brachiopods or
lamp shells)
Although, at first glance similar to bivalve clams, brachiopods are
radically different from the phylum Mollusca to which the clams belong
and bear no genetic relationship to them. Brachiopods have existed
since Cambrian time and the phylum, although much reduced, survives to
this day. The bulk of brachiopod species existed during Paleozoic
time and they are important index fossils for this period of time.
Brachiopods are organisms attached to the bottom (sessile) by a pedicle
and are bilaterally symmetrical. In contrast, clams tend to
be symmetrical along the hinge line and are only rarely bilaterally symmetrical.
There are two classes of brachiopods depending on whether the shell is
articulated (hinged) or not.
Class INARTICULATA
The two shells
are not hinged and are held together by muscles. Although
geologically unimportant, the genus Lingula holds the survival
record for an animal, having existed for over 500 million years since Cambrian
time.
Class ARTICULATA
The
two shells are hinged and generally more ornate. They make up the
bulk of fossil brachiopod species.